identifier	taxonID	type	CVterm	format	language	title	description	additionalInformationURL	UsageTerms	rights	Owner	contributor	creator	bibliographicCitation
93268783967C702CFDBDFBDDFB40FA02.text	93268783967C702CFDBDFBDDFB40FA02.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Cameroceras Conrad 1842	<div><p>Genus Cameroceras Conrad, 1842</p><p>Type species</p><p>Cameroceras trentonense Conrad, 1842, Middleville, New York, USA, Trenton Limestone, late Katian; by original designation.</p><p>Diagnosis</p><p>Slender, large orthocones with circular or somewhat depressed cross section; sutures simple and straight, or with very slight ventral lobe; siphuncle up to 0.5 of corresponding conch cross section in diameter; mostly marginally positioned; septal necks holochoanitic; endocones simple; endosiphuncular tube narrow, situated in half of siphuncle that is closer to conch margin. (Adopted from Teichert 1964a.)</p></div>	https://treatment.plazi.org/id/93268783967C702CFDBDFBDDFB40FA02	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783967C702BFDCCF9B6FC87FE36.text	93268783967C702BFDCCF9B6FC87FE36.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Cameroceras hasta (Eichwald 1857)	<div><p>Cameroceras hasta (Eichwald, 1857)</p><p>Figs 5A–B, 6</p><p>Endoceras hasta Eichwald, 1857: 194 .</p><p>Endoceras magnum Stumbur, 1956: 182–183, pl. 3 figs 2–3, text-fig. 4.</p><p>Rossicoceras pirguense Balashov, 1968: 113, pl. 15 figs 3–4.</p><p>Endoceras novomagnum Greenfield, 2023: 1790 .</p><p>Endoceras hasta – Eichwald 1860: 1247, pl. 46 fig. 7a–b.</p><p>Endoceras megastoma – Teichert 1930: 270, 273, pl. 5 fig. 1, text-fig. 2 (with synonymy).</p><p>Rossicoceras hasta – Balashov 1962a: pl. 4 fig. 4; 1968: 112, pl. 15 figs 1–2; 1974: 794, pl. 4 fig. 4. ― Saladzius 1966: 36, pl. 6 fig. 2. ― Dzik 1984: 35, text-fig. 7.32.</p><p>Endoceras magnum – Balashov 1968: 70.</p><p>Cameroceras hasta – Kröger 2013: 6–7, fig. 3.</p><p>Diagnosis</p><p>Smooth orthocones with a slightly depressed conch cross section; angle of expansion less than 5°; sutures directly transverse, seven or more chambers occur on a distance similar to the conch cross section; siphuncular diameter ca 0.5 of corresponding conch cross section; siphuncle slightly removed from conch wall; siphuncular segments slightly concave in lateral view; septal necks holochoanitic; endosiphocones form central spiculum. (Compiled from Balashov 1968.)</p><p>Material examined</p><p>ESTONIA • 2 specs; Hiiumaa Island, Kõrgessaare quarry; Vormsi Regional Stage; GIT 426-549, GIT 426-1111 • 4 specs; Paluküla quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-575, GIT 426-1102, 426-1104, GIT 878-127 • 1 spec.; Vormsi Island, Saxby old quarry; Kõrgessaare Formation, Pirgu Regional Stage; TUG 1745-240 • 1 spec.; Saaremõisa (Lyckholm); Kõrgessaare Formation, Vormsi Regional Stage; TUG 42-373 • 1 spec.; Vormsi Island, Saxby shore, Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-42 • 1 spec. from an unspecified locality at Vormsi Island, Kõrgessaare Formation, Vormsi Regional Stage; TUG 1650-1 .</p><p>Type locality and horizon</p><p>Saaremõisa (Lyckholm), N of Haapsalu, western Estonia; Kõrgessaare Formation, Vormsi Regional Stage, late Katian, Ordovician.</p><p>Description</p><p>Two specimens are relatively long, and well-preserved fragments of the phragmocone:</p><p>Specimen TUG 1745-240 (Fig. 5B) is a fragment of a phragmocone, which is slightly deformed and in which the outer shell is not preserved. The conch cross section was apparently circular. The conch height is 43–62 mm at a length of 125 mm (angle of expansion 9°). The sutures are narrowly spaced (at conch height 48 mm with chamber length of 4 mm, at conch height 62 mm with chamber length 5.5 mm, RCL = 0.08–0.09) and are directly transverse. At a conch height of 62 mm, the siphuncle is 7 mm from the conch margin, and 28 mm high (RSP = 0.21, RSH = 0.45). Where visible, the septal necks are holochoanitic. At a conch height of 45 mm, a symmetric endosiphocone is preserved, which has its tip at ca mid-height of the siphuncle, and which is ca 35 mm long. A similar symmetrical endosiphocone is preserved in specimen GIT 426-574 where the conch height is ca 50 mm, the siphuncular diameter is 21 mm. There, the cone is ca 45 mm long.</p><p>Specimen TUG 42-373 (Fig. 5A) is a well-preserved part of a phragmocone with a circular conch cross section and with parts of the smooth outer shell preserved. The conch has a diameter of 60–78 mm over a length of 110 mm (angle of expansion = 9°). The sutures are straight and directly transverse; at a conch height of 67 mm they are 8 mm apart (RCL = 0.12). The siphuncle is 33 mm heigh, where the conch height is 78 mm and positioned ca 15 mm from the conch margin (RSP = 0.33).</p><p>A compilation of measurements of the relative chamber length (RCL) and the relative siphuncular position (RSP) of the Estonian material shows the variability of respective values, resulting in a mean RCL of 0.09 (n= 10), and mean RSP of 0.24 (n = 7), respectively (Fig. 6).</p><p>Remarks</p><p>The species diagnosis given in Kröger (2013) was based on Balashov’s (1968) description of the holotype, in which the latter states that in the holotype, seven chambers occur per distance similar to the conch cross section (RCL ca 0.14). This is in contradiction to the figured holotype (Balashov 1968: pl. 15, fig. 1), where the RCL can be measured as ca 0.11. The RCL of the measured holotype is larger than the mean of the RCL’s from the material examined herein (RCL = 0.09) but still well within its variability (0.06–0.12). This applies also for the specimens assigned to C. hasta from the Boda Limestone, Sweden (Kröger 2013: 7). Accounting for this variability, the diagnosis given in Kröger (2013) is herein slightly emended with respect the relative chamber length.</p></div>	https://treatment.plazi.org/id/93268783967C702BFDCCF9B6FC87FE36	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783967B702BFDDFFDA9FED9F8A8.text	93268783967B702BFDDFFDA9FED9F8A8.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Cameroceras regulus (Eichwald 1860)	<div><p>Cameroceras regulus (Eichwald, 1860)</p><p>Fig. 5C</p><p>Endoceras regulus Eichwald, 1857: 177 .</p><p>Orthoceras turris Angelin in Angelin &amp; Lindström, 1880: 6, pl. 6 figs 14–15.</p><p>Endoceras iucundum Stumbur, 1956: 181, 182, pl. 1 fig. 4, pl. 2 fig. 1, text-fig. 3.</p><p>Endoceras regulus – Eichwald 1860:1248, pl. 46 fig. 8.</p><p>Cameroceras regulus – Balashov 1968: 70, 101, pl. 5 fig. 3. — Kröger 2013: 7–8.</p><p>Endoceras iucundum – Balashov 1968: 101.</p><p>Diagnosis</p><p>Orthocones with a slightly depressed conch cross section; angle of expansion less than 5°; ornamented with fine transverse striae; sutures directly transverse, ca seven chambers occur on a distance similar to the conch cross section; siphuncular diameter up to 0.5 of corresponding conch cross section; siphuncle marginal, in contact with shell wall; siphuncular segments slightly concave in lateral view; septal necks holochoanitic. (Adopted from Balashov 1968.)</p><p>Material examined</p><p>ESTONIA • 1 spec.; Harju County, Nõmmeküla quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 939-75 .</p><p>Type locality and horizon</p><p>Kõrgesaare, Hiiumaa Island, Estonia; Kõrgessaare Formation, Vormsi Regional Stage, late Katian, Ordovician.</p><p>Description</p><p>Specimen TUG 939-75 is a fragment of a phragmocone with parts of the outer shell preserved. The conch surface is smooth. The conch cross section is circular. The conch has a height of 33–34 mm at a length of 46 mm (angle of expansion = 1.2°). At the conch height of 34 mm the chamber length is 7 mm (RCL = 0.21). The siphuncle is marginally positioned with a diameter of 16 mm where the conch height is 34 mm. The septal necks are holochoanitic and form siphuncular segments, which have in longitudinal view slightly concave outlines (Fig. 5C). The siphuncle is filled with a massive sparitic infill, which preserved no details of the internal structure of the endosiphuncular deposits.</p><p>Remarks</p><p>The specimen can be identified as a C. regulus based on its large marginal siphuncle and its holochoanitic septal necks.</p></div>	https://treatment.plazi.org/id/93268783967B702BFDDFFDA9FED9F8A8	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396787028FDB6FE36FB68FD0F.text	9326878396787028FDB6FE36FB68FD0F.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Nybyoceras Troedsson 1926	<div><p>Genus Nybyoceras Troedsson, 1926</p><p>Type species</p><p>Actinoceras (Nybyoceras) bekkeri Troedsson, 1926 from Niibi, Estonia, Pirgu Regional Stage, late Katian; by original designation.</p><p>Diagnosis</p><p>Slender straight shell, eccentric siphuncle; adnation areas broad ventrally on posterior side of segments; dorsally on adoral side; septal necks very short and adnate to adoral surface of septa, endosiphuncular canal system reticulate to curved, branching radial canals. (Compiled from Teichert 1964.)</p></div>	https://treatment.plazi.org/id/9326878396787028FDB6FE36FB68FD0F	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396787029FDCEFCB7FBC2FCD1.text	9326878396787029FDCEFCB7FBC2FCD1.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Nybyoceras bekkeri Troedsson 1926	<div><p>Nybyoceras bekkeri Troedsson, 1926</p><p>Figs 7A, 8A–B</p><p>Actinoceras (Nybyocera s) bekkeri Troedsson, 1926: 106–107, pl. 63 figs 1–3.</p><p>Actinoceras bigsbyi Bronn aff. – Eichwald 1860: 1253–1255 (partim).</p><p>Nybyoceras bekkeri – Teichert 1930: 287–288, pl. 6 figs 7–8, pl. 7 fig. 19; 1933: 130, 149, 176; 1964a: K208, fig. 2a–c. ― Foerste &amp; Teichert 1930: 277, 279. ― Strand 1934: 62. ― Shimizu &amp; Obata 1936: 119. ― Balashov 1953a: 210 (faunal list only). ― Teichert &amp; Glenister 1953: 17–18. ― Stumbur 1956: 176. ― Flower 1957: 24. ― Sweet 1958: 48. ― Balashov &amp; Zhuravlyeva 1962: 218, fig. 16, pl. 1 fig. 12. ― Dzik 1984: 149, text-fig. 57.17. ― Lehmann 1987: 193–194, pl. 3 figs 28–29.</p><p>Nybyoceras bekkei (sic) – Barskov 1972: 81.</p><p>Diagnosis</p><p>Nybyoceras with eccentric position of the siphuncle (RSP = 0.25), and with widely expanded siphuncular segments (SCR ca 2–2.5); incipient annuli grow in apical direction on the adoral surface of the septa; fully developed annuli are asymmetrically developed in longitudinal direction and are heavier on the ventral side. (Compiled from Teichert 1930.)</p><p>Material examined</p><p>ESTONIA • 1 spec.; Vormsi Island, Saxby shore; Kõrgessaare Formation, Vormsi Regional Stage; GIT 939-47 • 1 spec.; Vormsi Island, Saxby shore (N); Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-1129 • 1 spec.; Saaremõisa (Lyckholm); Kõrgessaare Formation, Vormsi Regional Stage; TUG 1745-227 • 1 spec.; Sutlepa quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 47-870 • 1 spec.; Paluküla quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-1107 • 1 spec.; Kasari, Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-1120. (see also supplementary data 1) .</p><p>Type locality and horizon</p><p>Niibi, Estonia; Adila Formation, Pirgu Regional Stage.</p><p>Description</p><p>Specimen GIT 426-1107 (Fig. 8A) is a fragment of a phragmocone with a conch diameter of 66 mm, with a chamber length of 12 mm (RCL = 0.18) and a siphuncle, which is strongly expanded 24 mm in diameter (SCR = 2). The septal foramen is 7 mm wide. The connecting ring forms ventrally a wide (9 mm wide) area of adnation on the adoral surface of the septum and dorsally only a narrow (ca 3 mm wide) area of adnation on the adapical face of the septum. The septal necks are short and adnate. Incipient annuli grew in adapical direction and are more strongly developed on the ventral side of the conch.</p><p>Specimen GIT 426-1120 (Figs 7A, 8B) is a fragment of a phragmocone 125 mm long, and increasing in conch diameter 43–58 mm (angle of expansion= 7°), a circular conch cross section, a septal spacing with RCL of 0.2, and an RSP of 0.32. Specimen GIT 426-1129 is a fragment of a phragmocone 72 mm long, and increasing in conch diameter from 54–62 mm (angle of expansion= 6°), a septal spacing with RCL of 0.2, and an RSP of 0.23. Specimen TUG 1745-227 is a fragment of a phragmocone 78 mm long, and increasing in conch diameter 50–60 mm (angle of expansion= 7°), a septal spacing with RCL of 0.3, and an RSP of 0.33.</p><p>Remarks</p><p>The specimens assigned herein to N. bekkeri have an angle of expansion of 6–7°. This differs from the specimen figured in Teichert (1930: pl. 7 fig. 19), which expands with 12°. Because the angle of expansion is not known from the type-material (see Troedsson 1926), the diagnostic value of this character cannot be evaluated until more material from this species is known.</p></div>	https://treatment.plazi.org/id/9326878396787029FDCEFCB7FBC2FCD1	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396667034FDDAFEB0FC52FADF.text	9326878396667034FDDAFEB0FC52FADF.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Nybyoceras intermedium Teichert 1930	<div><p>Nybyoceras intermedium Teichert, 1930</p><p>Figs 7C, 8C–D, G, 9A</p><p>Nybyoceras intermedium Teichert, 1930: 288, 290, pl. 7 fig. 22.</p><p>Nybyoceras intermedium – Foerste &amp; Teichert 1930: 277. ― Teichert 1933: 149. ― Strand 1934: 63. ― Balashov 1953a: 210; 1975: 63–64, pl. 5 fig. 10. ― Stumbur 1956: 176. ― Flower 1957: 24. ― Saladzius 1966: tab. 1. ― Barskov 1972: 81.</p><p>Emended diagnosis</p><p>Nybyoceras ornamented with fine, wavy longitudinal lirae, with subcentral to eccentric siphuncle position (RSP 0.3–0.5), with moderately expanded siphuncular segments (SCR ca 1.5–2); incipient annuli grow in adoral direction on the adoral surface of the septa; fully developed annuli are asymmetrically developed in longitudinal direction and are heavier on the ventral side. (Compiled from Teichert 1930.)</p><p>Material examined</p><p>ESTONIA • 1 spec.; Hiiumaa Island; Kõrgessaare quarry, Vormsi Regional Stage; TUG 939-50 • 1 spec.; Paluküla quarry; Kõrgessaare quarry, Vormsi Regional Stage; GIT 426-573 • 1 spec.; Moe stratotype; Moe Formation, Pirgu Regional Stage; TUG 939-49 • 1 spec.; Pahkla; Moe Formation, Pirgu Regional Stage; TUG 1745-293. (See also supplementary data 1)</p><p>Type locality and horizon</p><p>Niibi, Estonia; Adila Formation, Pirgu Regional Stage.</p><p>Description</p><p>Specimen GIT 426-573 is a fragment of a phragmocone, its conch diameter cannot be measured because of its incomplete preservation. The connecting ring is not preserved. The septal necks are short armenoceratoid, adnate. The septal foramen is 4–5 mm wide where the chamber length is 9.5 mm. Incipient endosiphuncular annuli are developed ventrally along the adoral surface of the septum (Fig. 8C).</p><p>Specimen TUG 939-49 is a 98 mm long fragment of a phragmocone with a diameter of 26–43 mm (angle of expansion = 10°) which has a well-preserved conch surface. The surface is ornamented with fine wavy longitudinal lirae; ca seven of them occur per millimeter. The lirae produce a fine Zigzag pattern (Fig. 9A).</p><p>Specimen TUG 1745-293 (Fig. 8G) is a fragment of a phragmocone 46 mm long and increasing in conch diameter 21–29 mm (angle of expansion = 10°). In this length, eight chambers occur (RCL: 0.23– 0.24). The conch cross section is circular, and the surface is poorly preserved. The siphuncle is slightly eccentrically positioned (RSP: 0.45–0.46) and broadly expanded; where the conch diameter is 27 mm, one segment is 9.5 mm high and 6.2 mm long (SCR = 1.53) and the septal foramen has a diameter of ca 2 mm. The septal necks are short and adnate. The connecting ring forms wide adnate areas on the adapical surfaces of the septa. On the adoral surface of the septa the adnate area is only developed ventrally. Thick endosiphuncular deposits are present. These are more strongly developed on the adoral side of the septal foramen than the adapical side. Hypo- and episeptal cameral deposits are restricted to the ventral side of the siphuncle.</p><p>Specimen TUG 939-50 (Fig. 8D) is a fragment of a phragmocone with the internal characters preserved. Where the diameter is 23 mm, the chambers are 6 mm long (RCL = 0.26), the septal foramen is 2.8 mm in diameter, the connecting rings inflate to 9 mm in height (SCR = 1.5), and the septal necks are apparently short adnate. Thick, asymmetrically developed endosiphuncular annuli and thin mural, episeptal and hyposeptal deposits occur.</p><p>Remarks</p><p>Teichert (1930) distinguished N. intermedium from the two co-occurring species of Nybyoceras in the type locality Niibi by three features: (1) its narrower siphuncle (relative to the corresponding conch diameter), (2) its more centrally positioned siphuncle, and (3) unique growth pattern of the endosiphuncular annuli. The material available herein allows for a revision of Teichertʼs (1930) diagnosis:</p><p>(1) The relative siphuncular diameter of the type of N. intermedium is 0.31 compared to 0.55 in the specimen determined as N. bekkeri by Teichert (1930: pl. 7 fig. 19). However, often in actinocerids, complete conch cross sections are not available. Therefore, it is better to use the SCR for comparison, which is 1.6–1.9 in the type of N. intermedium, and 2.1–2.5 in the types of N. bekkeri (Troedsson 1926: pl. 63 figs 2–3).</p><p>(2) The figured specimens of the two species in Teichert (1930) differ only slightly in RSP with 0.30 in N. intermedium, and 0.26 in N. bekkeri . Two specimens, assigned here to N. intermedium, have subcentral siphuncle positions (TUG 939-49, 1745-293), where the conch diameter is between 20– 29 mm. In the type specimen, the more eccentric siphuncular position occurs at diameters&gt; 60 mm. This is interpreted here as an ontogenetic change in the siphuncular position, and it is included in the diagnosis of N. intermedium .</p><p>(3) Teichert (1930) distinguished N. intermedium from N. bekkeri based in the growth pattern of the endosiphuncular annuli. In N. intermedium, he found annuli, which initially grew toward the adoral side of the septal neck and septum. Little is known about the variability in the development of the annuli. When fully developed, the annuli of N. bekkeri and N. intermedium are virtually indistinguishable in dorsoventral median section as both exhibit stronger development the ventral adoral quadrant (compare Troedsson 1926: pl. 63 fig. 3). Additionally, the high potential for misleading interpretations of 3D-structures of endosiphuncular annuli have been described by Pohle et al. (2024) and Turek &amp; Aubrechtová (2024).</p><p>In conclusion, the relative expansion of the siphuncle seems to be the most reliable character to distinguish between N. bekkeri and N. intermedium . Also included in the diagnosis is the ornamentation, which is now known from this species from specimen TUG 939-49.</p></div>	https://treatment.plazi.org/id/9326878396667034FDDAFEB0FC52FADF	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396647035FDAEFA1BFC0EFE72.text	9326878396647035FDAEFA1BFC0EFE72.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Ormoceras Stokes 1840	<div><p>Genus Ormoceras Stokes, 1840</p><p>Type species</p><p>Ormoceras bayfieldi Stokes, 1840 from Niibi, Estonia; Adila Formation, Pirgu Regional Stage, late Katian; subsequent designation by Bassler (1915).</p><p>Diagnosis</p><p>Medium-sized straight shells, circular or nearly so in cross section; siphuncle subcentral; segments almost globular; septal necks short cyrtochoanitic; endosiphuncular canal system moderately complex to simple, few radial canals. (Adopted from Teichert 1964a.)</p></div>	https://treatment.plazi.org/id/9326878396647035FDAEFA1BFC0EFE72	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396657032FDBFFE07FACEFCF8.text	9326878396657032FDBFFE07FACEFCF8.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Ormoceras heckeri Teichert 1930	<div><p>Ormoceras heckeri Teichert, 1930</p><p>Fig. 8E</p><p>Ormoceras heckeri Teichert, 1930: 290, pl. 7 fig. 21.</p><p>Ormoceras heckeri – Balashov 1953a: 211. ― Stumbur 1956: 176. ― Flower 1957: 11.</p><p>Diagnosis</p><p>Straight shell with circular cross section; siphuncular position subcentral, siphuncular segments barrel-shaped, approximately as high as long (SCR ca 1); septal necks very short and adnate to adoral surface of septa ( Nybyoceras -like).</p><p>Material examined</p><p>ESTONIA • 2 specs; Paope quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 1745-280, TUG 1745-281 • 1 spec.; Vormsi Island, Saxby shore; Kõrgessaare Formation, Vormsi Regional Stage; TUG 1680-19 .</p><p>Type locality and horizon</p><p>Niibi, Estonia; Adila Formation, Pirgu Regional Stage.</p><p>Description</p><p>Specimen TUG 1680-19 (Fig. 8E) is a short fragment of the phragmocone without external characters preserved, with circular conch cross section and a diameter of 36 mm, the septa are ca 7 mm apart (RCL = 0.19), and the siphuncle is eccentrically positioned (RSP = 0.34). The septal necks are short adnate and the connecting ring forms barrel-shaped segments with a height of 8 mm (SCR = 1.14).</p><p>Specimen TUG 1745-281 is a fragment of a phragmocone 28 mm long, and increasing in diameter 20–23.5 mm (angle of expansion = 7°). The conch surface is not preserved. The sutures are directly transverse and straight with an RCL of 0.26. The septal foramen is nearly centrally positioned (RSP = 0.48) and has a diameter of 2 mm where the conch diameter is 22 mm. The septal necks are very short adnate, the connecting ring is not preserved.</p><p>Remarks</p><p>The species was described in detail by Teichert (1930). The new data suggest an ontogenetic change of the position of the siphuncle from central in early growth stages to eccentric in later growth stages.</p></div>	https://treatment.plazi.org/id/9326878396657032FDBFFE07FACEFCF8	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396627032FD46FCFBFC4DFA0E.text	9326878396627032FD46FCFBFC4DFA0E.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Ormoceras undefined-A	<div><p>Ormoceras sp. A</p><p>Fig. 8H</p><p>Material examined</p><p>ESTONIA • 1 spec.; Salu; Pirgu Regional Stage; TUG 1745-239 .</p><p>Description</p><p>Specimen TUG 1745-239 is a ca 113 mm long fragment of a phragmocone with a conch height of 23– 45 mm (angle of expansion = 11°) which is slightly deformed. The conch surface is apparently smooth. The RCL varies between 0.23–0.24 and at a conch height of 27 mm the RSP is ca 0.3. The septal necks are short adnate, and the connecting ring forms barrel-shaped siphuncular segments with a height of 5.8 mm where the length is 6.5 mm (SCR = 0.89). Incipient, symmetric endosiphuncular annuli occur where the conch height is 25 mm.</p><p>Remarks</p><p>The specimen differs from O. heckeri in having a less expanded siphuncle (SCR = 0.89 in specimen TUG 1745-239 compared with SCR&gt; 1 in O. heckeri) at comparable conch diameters. However, this single, fragmentarily preserved specimen does not allow for species level determination and detailed comparison with other, e.g., North American species of the genus.</p></div>	https://treatment.plazi.org/id/9326878396627032FD46FCFBFC4DFA0E	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396627033FDA9F9AAFEE5FC8B.text	9326878396627033FDA9F9AAFEE5FC8B.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Gorbormoceras Kröger 2025	<div><p>Genus Gorbormoceras gen. nov.</p><p>urn:lsid:zoobank.org:act: 923963A2-FF6F-4A62-8421-E6B8E2B10E76</p><p>Type species</p><p>Gorbormoceras vohilaidense gen. et. sp. nov., from Vohilaid shore (E), Vohilaid Island, Estonia; Adila Formation, Pirgu Regional Stage.</p><p>Diagnosis</p><p>Slightly exogastrically curved, nearly orthoconic longicones with a circular (or nearly so) conch cross section; ornamented with shallow annulation and distinct longitudinal lirae; sutures form shallow lateral lobes; ca five chambers occur at a length equal to corresponding conch cross section; siphuncle slightly eccentrically positioned; septal necks short or absent; siphuncular segments widely expanded with adnate areas at adoral and apical surfaces of septa; endosiphuncular and cameral deposits not known.</p><p>Etymology</p><p>Combination of the two genus names Gorbyoceras and Ormoceras, because the new genus, in a unique fashion, combines essential features of both genera.</p><p>Remarks</p><p>The new genus is provisionally assigned to the Ormoceratidae because of its subcentrally positioned, widely expanded siphuncle, and the very short recumbent or absent septal necks. Short or very short cyrtochoantitic to recumbent septal necks and widely expanded siphuncular segments are known from other ormoceratids, such as Ormoceras and Orthonybyoceras Shimizu &amp; Obata, 1935 .</p><p>Comparison</p><p>Troedssonoceras Foerste, 1928b is similar in having widely expanded siphuncular segments and a longitudinal ornamentation. In Troedssonoceras, the siphuncular shape is similar to Deiroceras (with cyrtochoanitic septal necks), and the connecting ring is not adnate (see, e.g., Flower 1946: 535). Eskimoceras Troedsson, 1926 has an annulated conch and widely expanded siphuncular segments. It differs from the new genus in having cyrtochoanitic septal necks and in lacking a longitudinal ornamentation.</p></div>	https://treatment.plazi.org/id/9326878396627033FDA9F9AAFEE5FC8B	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396637030FDFDFC2DFCDBFD3E.text	9326878396637030FDFDFC2DFCDBFD3E.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Gorbormoceras vohilaidense Kröger 2025	<div><p>Gorbormoceras vohilaidense gen. et. sp. nov.</p><p>urn:lsid:zoobank.org:act: 820DB1BC-79F4-40A5-A0B0-19D08C785DD6</p><p>Figs 7B, 8F</p><p>Diagnosis</p><p>Same as for genus, by monotypy.</p><p>Etymology</p><p>The name refers to Vohilaid Island, the type locality.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Vohilaid Island, Vohilaid shore (E); Adila Formation, Pirgu Regional Stage; GIT 878-235.</p><p>Description</p><p>The specimen is a slightly exogastrically curved mold of parts of a phragmocone and a body chamber. The conch cross section is apparently circular. At a conch diameter of 28–38 mm, the angle of expansion is 14°. At the base of the body chamber, the diameter is 31 mm. The preserved length of the body chamber is 60 mm. Although the outer shell is not preserved, traces of a relatively strong ornamentation with ca 20 longitudinal lirae around the circumference and a weak annulation are visible (Fig. 7B). Near the base of the body chamber, ca five annulations occur in a distance equal to the corresponding conch cross section.</p><p>The sutures form shallow lateral lobes and are slightly adorally shifted on the prosiphuncular side of the conch, the most adoral sutures are slightly crowded (chamber length 4.5 mm), at a conch height of 28 mm they are 6 mm distant (RCL = 0.21). The siphuncle is eccentrically positioned; near the apical end of the specimen, where the conch diameter is 31 mm, it is 10 mm distant from the conch margin and has a diameter of ca 3.3 mm (RSP = 0.36). The septal necks are short recumbent or achoanitic. The connecting ring is thin, and forms widely expanded segments with adnate areas at the adoral and apical septal surfaces (Fig. 8F). Where the septal foramen is 3.3 mm, and the chamber length is 4 mm, the segments expand toward a height of 8.6 mm (RSS = 2.15).</p><p>Remarks</p><p>This specimen is externally similar to Cycloceras fenestratum Eichwald, 1860 with regard to the general conch shape and its traces of the ornamentation (ca 20 longitudinal lirae and ca five annulations per distance equal to the corresponding conch cross section). However, it is larger (maximum diameter ca 25 mm in C. fenestratum) and has a larger angle of expansion (angle of expansion &lt;10° in C. fenestratum) (see e.g., Kröger 2013). Internally, the specimen is similar to species of Ormoceras .</p><p>Comparison</p><p>The widely expanded siphuncle and the ornamentation of the new species are most similar to Troedssonoceras (?) obscuriliratum Flower, 1946, from which it differs in having a more centrally positioned siphuncle and a weakly annulated conch. Another orthoconic species with a nodular ornamentation, comparable to G. vohilaidense sp. nov., is Spyroceras (?) nodosum Sweet &amp; Miller, 1957, from which the internal characters are not known.</p></div>	https://treatment.plazi.org/id/9326878396637030FDFDFC2DFCDBFD3E	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396607030FDCDFCDFFCC8FAF5.text	9326878396607030FDCDFCDFFCC8FAF5.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Pleurorthoceras Flower 1962	<div><p>Genus Pleurorthoceras Flower, 1962</p><p>Type species</p><p>Orthoceras clarksvillense Foerste, 1924 from Clarksville, Ohio, USA, Waynesville Formation, latest Katian; by original designation.</p><p>Diagnosis</p><p>Slender, gradually expanding, smooth orthocones; circular in cross section with straight, transverse sutures; chamber distance between one-third to one half of the corresponding conch diameter (RCL = 0.3–0.5); siphuncle subcentral to central; siphuncular segments subtubular, slightly expanded within chambers; septal necks short, suborthochoanitic; endosiphuncular deposits unknown; mural cameral deposits well developed. (Adopted from Flower 1962.)</p></div>	https://treatment.plazi.org/id/9326878396607030FDCDFCDFFCC8FAF5	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783966E703EFDF1FEB1FD8FFC8C.text	93268783966E703EFDF1FEB1FD8FFC8C.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Striatocycloceras Kroger & Isakar 2006	<div><p>Genus Striatocycloceras Kröger &amp; Isakar, 2006</p><p>Type species</p><p>Orthoceras undulostriatum Hall, 1847 from Middleville, New York, USA, Trenton Formation, late Katian; by original designation.</p><p>Diagnosis</p><p>Slender orthocones with circular or slightly compressed conch cross section, with asymmetrically curved septa and straight transverse or slightly oblique sutures; sutures parallel, or nearly so, to the annulations; annulations slightly irregularly spaced, with fine transverse ornament; siphuncle eccentric, narrow, tubular, or slightly expanded within the chambers; septal necks orthochoanitic; cameral and endosiphuncular deposits not known. (Adopted from Kröger &amp; Isakar 2006.)</p><p>Comparison</p><p>Anaspyroceras Shimizu &amp; Obata, 1935 differs from Striatocycloceras in having a fine longitudinal ornamentation. Leurocycloceras Foerste, 1928a is similarly ornamented to Striatocycloceras but differs in having long septal necks.</p></div>	https://treatment.plazi.org/id/93268783966E703EFDF1FEB1FD8FFC8C	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783966E703DFDDFFC28FAFCFDD1.text	93268783966E703DFDDFFC28FAFCFDD1.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Striatocycloceras hosholmense Kröger 2025	<div><p>Striatocycloceras hosholmense sp. nov.</p><p>urn:lsid:zoobank.org:act: 0530A9F0-1CC9-47F1-97C4-F5AB2352EE38</p><p>Figs 9C, 11E, G, 13B, D</p><p>Diagnosis</p><p>Annulated orthocones with circular conch cross section and nearly tubular conch at conch diameters&gt; 20 mm; ornamented with three to four annulations in a distance equal to the corresponding conch diameter; annulations straight transverse, regularly spaced and with sharp narrow crests; ornamented with ca 10–12 fine transverse growth lines or striae per cycle of annulation; suture lines in the troughs of the annulations and equally spaced to annulations; parallel sutures and annulations; RCL ca 0.25–0.3; siphuncle central, tubular to slightly expanded; septal foramen approximately one tenth of the diameter, septal necks orthochoanitic; shallow endosiphuncular deposits at position of septal necks; cameral deposits not known.</p><p>Etymology</p><p>Refers to the type locality, Hosholm shore, Vormsi Island.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Vormsi Island, Hosholm shore; Adila Formation, Pirgu Regional Stage; GIT 878-297.</p><p>Paratypes</p><p>ESTONIA • 5 specs; same collection data as for holotype; GIT 878-288, GIT 878-290, GIT 378-302, GIT 878-304, GIT 878-312 • 1 spec; same collection data as for holotype; TUG 1819-102 .</p><p>Description</p><p>The holotype is an 81 mm long fragment of a phragmocone with a circular conch cross section, and a conch-diameter of 24–25 mm (Fig. 13B). Three to four annulations occur in a distance equal to the corresponding diameter. The entire fragment has 11 equally spaced, directly transverse annulations. The annulations have deep rounded troughs (1.5 mm deep) and sharp, and narrow crests. The conch surface is ornamented with ca 12 transverse growth-lines per annulation (Fig. 9C). The sutures are positioned in the troughs of the annulations. The curvature of the septa is ca 3 mm deep with a slightly eccentric septal foramen, ca 2.5 mm in diameter. The siphuncle is nearly tubular, centrally positioned, slightly constricted at the position of the septal foramen. The septal necks are orthochoanitic, ca one millimeter long. At the position of the septal necks thin endosiphuncular annuli are developed (Fig. 11E). Cameral deposits are not developed.</p><p>A second specimen, GIT 878-312, is a fragment of a phragmocone with internal characters well-preserved. The fragment has a length of 68 mm, a diameter of 22–23 mm, and nine annulations and chambers (Fig. 13D). The siphuncle is nearly tubular with a diameter of ca 2.5 mm. The septal necks are orthochoanitic with a length of ca one millimeter, and thin endosiphuncular deposits are developed at the position of the septal necks. The siphuncle is nearly central. The angles of expansion of all specimens assigned to this species are less than 5° (Fig. 11G).</p><p>Remarks</p><p>The shell surface is poorly preserved in all specimens which are available for this study. The outer shell is commonly firmly attached to the matrix, covering the surface of the conch, obscuring fine detail of the ornamentation. Where the outer shell is visible, no longitudinal ornamentation is visible. However, it cannot be excluded that in this species very fine, sub-millimetre, longitudinal lirae are present on the shell surface. Therefore, S. hosholmense sp. nov. should also be compared with species of Anaspyroceras Shimizu &amp; Obata, 1935 (see: Flower 1943b: 115, and Sweet 1964c: K230, for a genus diagnosis of Anaspyroceras). Anaspyroceras is an annulated orthocerid, which is internally similar to Striatocycloceras but has a fine longitudinal ornament.</p><p>Comparison</p><p>The holotype of this species shows great similarity to the specimen figured in Dzik (1984: pl. 35 fig. 4a–c); subsequently designated as the holotype of Orthoceras clathrato - annulatum Roemer, 1861 therein. However, inconsistencies between Roemer’s (1861) figures and descriptions, and differences between Roemer’s (1861) and Dzik’s (1984) specimens indicate that Roemer’s (1861) type material for O. clathrato - annulatum consisted of multiple species. The specimen figured in Dzik (1984) has no outer shell preserved and the internal characters remain unknown. Further study of Roemer’s (1861) type material is needed to solve this problem (see also discussion under Gorbyoceras clathratoannulatum).</p><p>Striatocycloceras hosholmense sp. nov. differs from S. undulatostriatum, and S. foerstei (Teichert, 1930) in having a relatively wide annulation of three to four annuli per distance equal to the corresponding conch cross section, compared to more than four annuli in the latter two species. Additionally, endosiphuncluar annuli are not known from the latter two species. S. romingeri (Foerste, 1932) has a smaller adult size (only ca 10 mm) than S. hosholmense, and in S. obliquum (Eichwald, 1860), the annulation is oblique.</p><p>Several species of Anaspyroceras are similar to S. hosholmense sp. nov. but differ in the following aspects: A. anellus (Conrad, 1843) and A. paquettense (Foerste, 1932) differ in having narrower annulations (ca 5–6 annulations per distance equal to the corresponding conch cross section) and in being ornamented with fine longitudinal lirae. Anaspyroceras anzaas Teichert &amp; Glenister, 1953 has a low annulation and is ornamented with 26–33 longitudinal lirae. Anaspyroceras cylindricum Foerste, 1932 differs in having obliquely transverse annulations. Anaspyroceras cumberlandense Flower, 1946 has a narrower annulation and an irregularly nodose ornamentation. Anaspyroceras williamsae Flower, 1946 is ornamented with longitudinal lirae. The annulation of A. obscurum (Barrande, 1868) is less pronounced and narrower (&gt; 10 annulations at distance equal to the corresponding conch cross section).</p></div>	https://treatment.plazi.org/id/93268783966E703DFDDFFC28FAFCFDD1	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783966D703BFDBDFDE2FE65FE8D.text	93268783966D703BFDBDFDE2FE65FE8D.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Striatocycloceras hosholmense Kröger 2025	<div><p>Striatocycloceras cf. hosholmense</p><p>Figs 11F, 13C</p><p>Material examined</p><p>ESTONIA • 3 specs; Vormsi Island, Hosholm shore; Adila Formation, Pirgu Regional Stage; TUG 899- 81, TUG 939-20, TUG 1745-233.</p><p>Description</p><p>Specimen TUG 939-20 is a fragment of a phragmocone, 38 mm long, with diameter 23–27 mm (apical angle 8.5°), and four chambers and annulations (Fig. 13C). The characters of the outer shell are not preserved. The annulations are directly transverse with deep troughs and sharply accentuated crests. The sutures are parallel to and positioned in the troughs of the annulations. The siphuncle is nearly centrally positioned and slightly expanded within the chambers. It is ca 2.5 mm wide at position of the septal foramen and 3.5 mm wide at mid-way between septa. The septal necks are orthochoanitic, 1.3 mm long (Fig. 11F). No cameral deposits are developed. Two additional specimens are in the Estonian collections which are similar in having a sharply crested annulations, ca three annulations per distance equal to the corresponding conch diameter and an apical angle of ca 10°.</p><p>Remarks</p><p>The specimens described as Striatocycloceras cf. hosholmense are in all aspect similar to Striatocycloceras hosholmense sp. nov. expect in having a distinctly larger apical angle at comparable conch diameters. However, none of the specimens has its outer shell preserved, making a comparison somewhat questionable. More material is needed to establish this group of specimens as a distinct species. Notably, a similar pair of species A. anellus and A. paquettense with low and high apical angles are known from Katian strata of North America (Foerste 1932: 104). This could indicate the presence of sexual dimorphism in this genus.</p></div>	https://treatment.plazi.org/id/93268783966D703BFDBDFDE2FE65FE8D	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396687038FE14FB5DFED3F96A.text	9326878396687038FE14FB5DFED3F96A.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Palaeodawsonocerina Kroger & Isakar 2006	<div><p>Genus Palaeodawsonocerina Kröger &amp; Isakar, 2006</p><p>Type species</p><p>Spyroceras senckenbergi Teichert, 1930, Saaremõisa (Lyckholm), N of Haapsalu, Kõrgessaare Formation, Vormsi Regional Stage; by original designation.</p><p>Diagnosis</p><p>Straight or slightly cyrtoconic, circular or subcircular shell, with prominent, narrowly spaced annulations, growth lines, and numerous subordinate filiform longitudinally raised lines, producing a fine reticulate pattern; siphuncle central or slightly eccentric, slightly expanded, with achoanitic to very short orthochoanitic septal necks; apex blunt, slightly cyrtoconic, annulated. (Adopted from Kröger &amp; Isakar 2006.)</p></div>	https://treatment.plazi.org/id/9326878396687038FE14FB5DFED3F96A	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396687006FE2FF90EFB05FD9B.text	9326878396687006FE2FF90EFB05FD9B.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Palaeodawsonocerina senckenbergi (Teichert 1930)	<div><p>Palaeodawsonocerina senckenbergi (Teichert, 1930)</p><p>Figs 9B, 13A, 14</p><p>Spyroceras senckenbergi Teichert, 1930: 280, pl. 5 figs 3–4.</p><p>Spyroceras saxbyense Stumbur, 1956: 180, pl. 1 fig. 1.</p><p>Spyroceras sp. A – Strand 1934: 21, pl. 3 fig. 7.</p><p>Gorbyoceras duncanae – Balashov 1975: 68, pl. 1 figs 3–6.</p><p>Spyroceras senckenbergi – Dzik 1984: 122, 125, pl. 35 fig. 5, text-figs 48a, 49.20.</p><p>Gorbyoceras? senckenbergi – Kiselev 1991: 92, pl. 1 fig. 2.</p><p>Palaeodawsonocerina senckenbergi – Kröger &amp; Isakar 2006: 154–156, figs 8a, 10i, 12d–e. ― Kröger 2013: 34–36, figs 12a, 13ca. ― Pohle et al. 2022: fig. 2.</p><p>Diagnosis</p><p>Slightly compressed orthocones with very low apical angle of approximately 1°–2°; adult dorsoventral diameter approximately 25 mm; ornamented with five to six annulations in a distance that equates to the corresponding shell diameter in adult specimens; annulations straight or very slightly oblique to the normal of the conch axis and regularly spaced; very fine growth lines, about 50 per cycle of annulations; very fine longitudinal striae or raised lines, about five to seven per mm; suture line at the ridges of the annulations; parallel sutures and annulations; siphuncle central, slightly expanded within the chamber; septal foramen about 0.07 of the shell diameter. (From Kröger &amp; Isakar 2006.)</p><p>Material examined</p><p>ESTONIA • 1 spec.; Aulepa quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 895-150 • 3 specs; Harilaid; Vormsi–Pirgu regional stages; TUG 1745-241 to TUG 1745-243 • 1 spec.; Hosholm shore; Adila Formation, Pirgu Regional Stage; TUG 939-78 • 1 spec.; Kersleti quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 1745-17 • 2 specs; Kõrgessaare quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-30, GIT 426-49 • 5 specs; Moe trench; Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-103, GIT 878-105, GIT 878-110, GIT 878-111, GIT 878-112 • 1 spec.; Mõnuste quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-8 • 4 specs; Paluküla quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-62, GIT 426-65, GIT 426-87, GIT 426-88 • 2 specs; same data as for preceding; TUG 1745-20, TUG 1745-21 • 3 specs; Paope quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-29, GIT 426-563, GIT 426-564 • 1 spec.; same data as for preceding; TUG 1745-18 • 1 spec.; Saaremõisa (Lyckholm); Kõrgessaare Formation, Vormsi Regional Stage; TUG 1745-283 • 4 specs; same data as for preceding; GIT 878-119 to GIT 878-121, GIT 878- 124 • 2 specs; Saxby old quarry; Moe Formation, Pirgu Regional Stage; TUG 1745-218, TUG 939-28 • 30 specs; Saxby shore; Kõrgessaare Formation, Vormsi Regional Stage; TUG 939-28, TUG 1745-264, TUG 1666-12, TUG 1745-226, TUG 1745-251, TUG 1745-255, TUG 1745-256, TUG 1745-261 to TUG 1745-272, TUG 1745-321, TUG 1837-82, TUG 38-815, TUG 39-777, TUG 39-792, TUG 939- 17, TUG 939-19, TUG 939-27, TUG 939-73, TUG 939-81, TUG 939-82 • 4 specs; same data as for preceding; GIT 426-96 to GIT 426-99 • 16 specs; Saxby shore (N); Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-1125, GIT 426-1126, GIT 426-1131, GIT 426-24, GIT 426-42, GIT 426- 43, GIT 878-32 to GIT 878-35, GIT 878-37, GIT 878-51, GIT 878-53, GIT 878-54, GIT 878-72, GIT 878-81 • 2 specs; Sutlema quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-134, GIT 878-162 • 1 spec.; Urge quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 939-18 • 1 spec.; Vormsi Island; Kõrgessaare Formation, Vormsi Regional Stage; TUG 42-283 .</p><p>Type locality and horizon</p><p>Saaremõisa (Lyckholm), N of Haapsalu; Kõrgessaare Formation, Vormsi Regional Stage.</p><p>Remarks</p><p>Previous descriptions of this common species in the Vormsi Regional Stage strata of Estonia focused on well-preserved features of mature specimens, including the siphuncle, septal necks (Kröger &amp; Isakar 2006), and ornamentation (Kröger 2013). Here, new data about the variability of the angle of expansion, and ornamentation (Figs 9B, 13A) complement this knowledge, permitting the synonymy of Spyroceras sp. A of Strand (1934) with P. senckenbergi, because of its general similarity in conch shape and ornamentation. Also, based on the new data, and in contrast to previous lists of synonymies, Spyroceras senckenbergi in Dzik (1984) is synonymised with P. senckenbergi .</p><p>The data show that the angle of expansion tends to decrease with increasing conch size, being almost tubular in adult stages and up to 4–5° in juvenile growth stages (Fig. 13A). The largest specimen in the collection, specimen GIT 878-112, is a short fragment of a body chamber with a diameter of 30 mm. Only three specimens (GIT 878-53, GIT 878-112, TUG 1745-263) of the total collection (n= 89) have a diameter of more than 26 mm. This suggests an approximate adult size of the species of ca 25–30 mm.</p><p>It has been observed that the relative spacing of the annulation in P. senckenbergi decreases with conch size although it was not possible to substantiate quantitatively (Kröger &amp; Isakar 2006). Here, based on measurements from 22 specimens, it can be shown that there is no ontogenetic trend in relative annulation distance in P. senckenbergi (Fig. 14B–C). The spacing of the annulation varies between 1–6 mm in all specimens, it is widest in fragments of mature specimens (Fig. 14B).</p></div>	https://treatment.plazi.org/id/9326878396687006FE2FF90EFB05FD9B	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396567007FD86FD1DFA9FFE69.text	9326878396567007FD86FD1DFA9FFE69.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Palaeodawsonocerina Kroger & Isakar 2006	<div><p>Palaeodawsonocerina ? sp.</p><p>Fig. 12K</p><p>Material examined</p><p>ESTONIA • 1 spec.; Hosholm shore; Adila Formation, Pirgu Regional Stage; TUG 939-78 .</p><p>Description</p><p>The specimen is a ca 39 mm long, 18–20 mm high, orthoconic fragment (angle of expansion 3°) of a phragmocone with well-preserved shell sculpture. The conch cross section is slightly deformed. The conch is annulated with ca four annulations in a distance equal to the corresponding conch cross section. The annulations are directly transverse. The conch is ornamented with ca 60 fine longitudinal lirae around the circumference and subordinate transverse growth lines or lirae, producing a reticulate pattern (ca 10 transverse lirae per annulation). The septa are only partially preserved, the siphuncle and septal necks are not preserved. The sutures are positioned in the troughs of the annulations and are directly transverse parallel to the annulations.</p><p>Remarks</p><p>The finely reticulate ornamentation and the general conch shape of this specimen is similar to other species assigned to P. senckenbergi . It differs from the latter in having a wider spacing of its longitudinal lirae (1 mm and 60 lirae around circumference versus five to seven lirae per mm in P. senckenbergi). The fragmentary preservation of the internal characters leaves the genus level determination questionary because a similar fine reticulate ornamentation is known from Anaspyroceras, and Gorbyoceras (see e.g., Flower 1943b). Possibly, the specimen belongs to the same species as a specimen described by Strand (1934: 21) under G. clathratoannulatum, also ornamented with ca 60 longitudinal lirae.</p></div>	https://treatment.plazi.org/id/9326878396567007FD86FD1DFA9FFE69	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396577007FDDDFDA1FCFFFAA9.text	9326878396577007FDDDFDA1FCFFFAA9.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Ephippiorthoceras Foerste 1924	<div><p>Genus Ephippiorthoceras Foerste, 1924</p><p>Type species</p><p>Orthoceras formosum Billings, 1857, from English Head, Anticosti Island, Quebec, Canada, English Head formation, zone 3 or 4 (Foerste 1928c) (= Vauréal Formation, see Achab et al. 2011), late Katian; by original designation.</p><p>Diagnosis</p><p>Orthocones with circular to slightly compressed conch cross section; smooth or ornamented with fine transverse and /or longitudinal striae and lirae or coarse oblique plications; sutures form distinct broad lateral lobes; siphuncle subcentral to central, cyrtochoanitic septal necks; siphuncular segments expanded slendering adorally, parietal endosiphuncular deposits occur. (Compiled from Flower 1962, and Sweet 1964c.)</p><p>Remarks</p><p>Flower (1962: 33) assigned Ephippiorthoceras into his newly erected Proteoceratidae and justified it, without being more specific, among other arguments with the comment “other material indicates adoral slendering of the segments of the siphuncle.” Sweet (1964c: K256) assigned the genus with question into the Proteoceratidae and remarked that: “Details of the interior are not known in the type-species […] Ephippiorthocras is probably a pseudorthoceratid rather than a proteoceratid.” The material described herein suggests that Flower’s (1962) original evaluation was correct. In the Estonian specimens, a clear tendency for proteoceratid-like “slendering” is apparent. Moreover, the position of the siphuncle becomes more eccentric in later growth stages (see below).</p></div>	https://treatment.plazi.org/id/9326878396577007FDDDFDA1FCFFFAA9	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396577003FDC1FACBFAC2FBA3.text	9326878396577003FDC1FACBFAC2FBA3.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Ephippiorthoceras vormsiense Kröger 2025	<div><p>Ephippiorthoceras vormsiense sp. nov.</p><p>urn:lsid:zoobank.org:act: 9A7BEADF-FA56-4756-9CAE-D36E2CDCF182</p><p>Figs 15A–C, 16A–B, 17</p><p>Diagnosis</p><p>Faintly exogastrically curved longicones to orthocones with an angle of expansion of up to 9°; lateral sutural lobes shifted slightly adorally at venter; mature conch height ca 38–40 mm, with maximum height reached near the base of the mature body chamber or at adoral-most part of the mature phragmocone; mature body chamber ca 90 mm long and constricted; siphuncular position subcentral in early growths stages, eccentric in latest growth stages; siphuncle fusiform, expanded in early growth stages and nearly tubular in latest growth stages with septal necks changing from cyrtochoanitic to suborthochoantic during ontogeny.</p><p>Etymology</p><p>Refers to the type locality, Vormsi Island.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Vormsi Island, Hosholm shore (tower locality), Adila Formation, Pirgu Regional Stage; GIT 878-192.</p><p>Paratypes</p><p>ESTONIA • 2 specs; same collection data as for holotype; GIT 878-195, GIT 878-228 • 2 specs; Vohilaid Island, Vohilaid shore (E), Adila Formation, Pirgu Regional Stage; GIT 878-193, GIT 878-194 • 2 specs; same data as for preceding; TUG 1745-28, TUG 1743-75 .</p><p>Description</p><p>The holotype (GIT 878-192) (Fig. 15A) is the largest specimen, it reaches a conch height of 40 mm ca 25 mm adapically of the last septum on phragmocone. There, the conch width is 33 mm (CHI = 1.21). The phragmocone decreases in height and width toward 39 mm, 32 mm, respectively at the base of the body chamber. Only the basal ca 60 mm of the body chamber are preserved, they indicate a decreasing height toward the aperture. The sutures form a marked lateral lobe and have a distance of 7 mm (the adoralmost chamber) to 9 mm (RCL up to 0.23). The septal foramen is subcentral with a RSP of 0.39 at a conch height of 39 mm.</p><p>The mature body chamber is preserved in three specimens (GIT 878-192, GIT 878-194, GIT 878-228). Specimen GIT 878-228 (Fig. 15B) is a fragment of a phragmocone and a nearly complete mature body chamber, which is slightly deformed. At the base of the body chamber, the height and width are 35 mm, 37 mm respectively (CHI 0.95). The body chamber has a length of 90 mm and continuously decreases in diameter toward the aperture, where the width is 33 mm. The adapical ca 5 mm are constricted and apparently a ca 15 mm deep hyponomic sinus occurs on the prosiphuncular side. The adoralmost chamber of the phragmocone has a length of 4 mm, further adapicallly the sutures are 7 mm distant (RCL = 0.19). The sutures form a deep lateral lobe and are slightly more adorally located on the prosiphuncular side (the side with the hyponomic sinus) than on the opposite side. The preserved part of the phragmocone has an angle of expansion of 3° at a width of 35–37 mm. The septal foramen is nearly centrally positioned.</p><p>Specimen GIT 878-194 is a mold of a mature body chamber with a conch height and width at its base of 36 mm, 28 mm respectively (CHI = 1.29) and a preserved length of 70 mm. The height and width decrease adorally until at a point ca 45 mm from the base, the height is 31 mm. Further toward the aperture the height increases slightly, resulting in a body chamber outline with concave margins. The septal foramen at the last septum is subcentral (RSP = 0.33).</p><p>Specimen TUG 1743-75 is a slightly curved fragment of a phragmocone with heights of 23–31 mm and an angle of expansion of 9°, The sutures form distinct lateral lobes and are 5 mm apart at a conch height of 23 mm and 7 mm at a conch height of 30 mm (RCL: 0.22–0.23).</p><p>Measurements of the position of the septal foramen indicate a slight marginal shift of the siphuncle during growth with an RSP of 0.43 at a conch height of 23 mm (TUG 1745-286), toward and RSP of 0.38–0.39 at a conch height of 38–39 mm (GIT 878-192, GIT 878-193). The details of the siphuncle and septal neck are preserved in specimens GIT 878-192, GIT 878-193, and TUG 1745-28 (Fig. 16A–B). They reveal that the septal necks are cyrthochoanitic at earlier growth stages (conch heights &lt;33 mm) and suborthochoanitic near maturity (conch height 36–39 mm). The siphuncular segments are expanded fusiform in early growth stages and nearly tubular in later growth stages (Table 1).</p><p>Comparison</p><p>Ephippiorthoceras vormsiense sp. nov. has a smooth, or nearly so, conch surface, which differs from species which have a wrinkled or lirate ornamentation such as E. laddi Foerste, 1935b, E. formosum, Ephippiorthoceras plicatuloides Strand, 1934 (see also below), E. plicatulum Foerste in Twenhofel, 1928, E. schucherti Foerste, 1928c, E. tenuistriatum Foerste, 1935b . Ephippiorthoceras altocameratum Foerste, 1928c, and E. sieboldi (Billings, 1866) reach larger adult sizes (conch heights more than 55 mm at base of mature body chamber) (Foerste 1928c). Ephippiorthoceras compressum Foerste, 1928b differs in having strongly obliquely sloping sutures and a very low angle of expansion. Ephippiorthoceras decorum Teichert &amp; Glenister, 1953 differs in having cameral and endosiphuncular deposits and a clearly more eccentrically positioned siphuncle. The siphuncle of E. modestum Troedsson, 1926 is more centrally positioned.</p><p>Strand (1934) described two species of Ephippiorthoceras from late Katian strata of Norway ( E. plicatuloides Strand, 1934, E. frognoyense Strand, 1934). Details of the siphuncle and septal necks are unknown for either species. The two species are similar to E. vormsiense sp. nov. in size and suture shape but differ in having more narrowly spaced chambers (RCL = 0.13–0.14 in E. frognoyense) and have conspicuously wrinkled conchs ( E. plicatuloides). Both species are known from one or two specimens only, making comparisons with the Estonian material difficult. The narrow chamber spacing could be interpreted as an effect of maturity, but the wrinkled surface is known from other species of the genus (see above). A synonymy of E. vormsiense with one of the Norwegian species is therefore unlikely.</p></div>	https://treatment.plazi.org/id/9326878396577003FDC1FACBFAC2FBA3	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396537001FDE5FBD6FA85FE36.text	9326878396537001FDE5FBD6FA85FE36.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Gorbyoceras Shimizu & Obata 1935	<div><p>Genus Gorbyoceras Shimizu &amp; Obata, 1935</p><p>Type species</p><p>Orthoceras gorbyi Miller in Miller &amp; Faber, 1894, from Franklin County, Indiana, probably Saluda Formation, latest Katian, USA; by original designation.</p><p>Diagnosis</p><p>Slender, circular or slightly compressed orthocones with symmetrically curved septa and straight transverse sutures; sutures parallel to annulations in each groove of the annulations; annulations with fine transverse ornament or growth lines; annulations more prominent in adult growth stages; distinct irregularly spaced longitudinal ridges that may form nodes at the ridges of the annulations; siphuncle subcentral, expanded in early growth stages, with short cyrtochoanitic septal necks, nearly tubular in later growth stages, with suborthochoanitic septal necks; mural cameral deposits developed much farther anteriorly than endosiphuncular deposits. (Adopted from Kröger 2013.)</p><p>Remarks</p><p>Gorbyoceras and Dawsonoceras share many similarities. Following the diagnosis in the Treatise (Sweet 1964c), both are slender, annulated, orthocones with a transverse and longitudinal ornamentation; in both genera species with curved mature growth stages occur; in both genera the siphuncle is centrally positioned or nearly so, and tubular to slightly expanded; and in both genera the septal necks are very short, varying between achoanitic to suborthochoanitic to very short cyrtochoanitic, and small endosiphuncular annuli occur. The asserted difference between the two genera is the shape of the siphuncle and its ontogenetic change (Flower 1946; Sweet 1964c). In G. gorbyi and closely related species, such as G. grossi Flower, 1946, the siphuncle is clearly expanded (Flower 1946: 146). Flower (1946: 144–145) emphasized the ontogenetic variability of the siphuncular segments of species of Gorbyoceras . In several of them, “in general the outline of the segments becomes gerontically simplified, approaching an orthochoanitic condition […]” (Flower 1946: 145). Therefore, Gorbyoceras is placed within the Proteoceratidae of the Pseudorthocerataceae in the Treatise (Sweet 1964c: K256). In contrast, Frey (1995: P63) stated that no evidence exists for an ontogenetic change of siphuncular segments from expanded barrel-shape to subcylindrical in Gorbyoceras, and thus questioned the classification of Gorbyoceras within the Proteoceratidae .</p><p>The siphuncular segments of the Dawsonoceras are described as subcylindrical, and as “abruptly constricted at septal foramina” (Sweet 1964c: K238). Therefore, in the Treatise, Dawsonoceras as type of the Dawsonoceratida is placed within the Orthoceratacaea (Sweet 1964c: K238). However, the shapes of the siphuncle and septal necks are not known from the type-species D. hyatti (see Foerste 1928a: 273– 276, and Foerste 1928b: 28–29). In the Treatise, the illustrated details of the siphuncle and septal necks of Dawsonoceras are taken from Flower (1946: fig. 11), which is a generalized scheme not attributable to a specific species. The concept of Dawsonoceras in Sweet (1964c) was largely adopted by Kröger &amp; Isakar (2006) and in later publications (Kröger 2007, 2013), placing the Late Ordovician Cycloceras fenestratum Eichwald, 1860 into Dawsonoceras .</p><p>However, Sweet (1964c) and Kröger &amp; Isakar (2006) were not aware of, or ignored, Horny’s (1956) revision of Dawsonoceras . In this revision, a much narrower concept of Dawsonoceras was suggested, restricting the genus to annulated forms with a frilled ornamentation (Horny 1956: 462). Furthermore, Horny (1956: pl. 3 figs 2–4) described and illustrated the details of the well-preserved siphuncle and septal necks of specimens closely related to the Silurian type of Dawsonoceras ( D. hyatti), and type material of D. annulatum (Sowerby, 1816) from the British Wenlock. The siphuncle of these specimens is tubular, slightly expanded into the chambers, and adnate to the septa, and the septal necks are very short achoanitic or cyrtochoanitic. Hence, the ornamentation and the internal details of Ordovician species attributed to Dawsonoceras, such as Cycloceras fenestratum Eichwald, 1860 (Kröger &amp; Isakar 2006: fig. 8b; Kröger 2013: fig. 13a) differ considerably from the Silurian material described by Horny (1956) and are outside of his diagnosis of Dawsonoceras .</p><p>Accepting Horny’s (1956) diagnosis has consequences for recent approaches to classifying Dawsonoceras and Gorbyoceras (Pohle et al. 2022), which were based on descriptions of specimens assigned to C. fenestratum and G. textumamareum (Roemer, 1861) by Kröger &amp; Isakar (2006) and Kröger (2013). Therein, Gorbyoceras was placed within the Dawsonoceratidae (Pohle et al. 2022) .</p><p>Here, Horny’s (1956) diagnosis is accepted. Therefore, C. fenestratum (probably together with the similarly ornamented D. gregarium Kröger et al., 2011) need to be assigned to a genus other than Dawsonoceras (a task beyond the scope of this paper). Moreover, the Estonian material studied herein, supports Flowerʼs (1946) opinion that the siphuncle of Gorbyoceras changes from an expanded barrel shape towards subcylindrical (see Remarks chapter of G. textumamareum) during ontogeny, and hence the genus is best classified within the Proteoceratidae as suggested earlier (e.g., Sweet 1964c).</p></div>	https://treatment.plazi.org/id/9326878396537001FDE5FBD6FA85FE36	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
932687839651700FFE5CFE42FBC4FB42.text	932687839651700FFE5CFE42FBC4FB42.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Gorbyoceras clathratoannulatum (Roemer 1861) Kröger 2025	<div><p>Gorbyoceras clathratoannulatum (Roemer, 1861) comb. nov.</p><p>Figs 11B–C, 12C, H, 18</p><p>Orthoceras clathrato-annulatum Roemer, 1861: 57–58, pl. 7 figs 4a–b.</p><p>Orthoceras clathrato-annulatum – Roemer 1885: 52, 67, fig. 10a–b, pl. 3 fig. 10. ― Rüdiger 1889: 51–52, 85. ― Sauramo 1929: 8, 10. ― Dzik 1984: pl. 35 fig. 4a–c.</p><p>Spyroceras clathrato-annulatum – Teichert 1930: 278, 280, pl. 5 fig. 5. ― Balashov 1953a: 212.</p><p>Spyroceras cf. clathrato-annulatum – Strand 1934: 21 (partim).</p><p>Diagnosis</p><p>Annulated orthocones with circular conch cross section; adult conch diameter ca 20 mm; mature body chamber with decreasing conch diameter toward aperture and slightly bent against adapical conch part; ornamented with three to four annulations in a distance equal to the corresponding conch diameter; annulations straight transverse or very slightly oblique and slightly irregularly spaced; ornamented with ca 30 fine longitudinal and subordinate transverse lirae, about 10–15 transverse lirae per cycle of annulations; suture lines located in the troughs of the annulations and equally spaced as annulations; parallel sutures and annulations; siphuncle central, barrel-shaped, expanded in early growth stages, nearly tubular in late growth stages; septal foramen approximately one tenth of the diameter, septal necks short cyrtochoanitic to suborthochoanitic, endosiphuncular and cameral deposits not known.</p><p>Material examined</p><p>ESTONIA • 1 spec.; Vormsi Island, Hosholm shore; Adila Formation, Pirgu Regional Stage; GIT 840- 138 • 3 specs; same data as for preceding; TUG 899-80, TUG 1445-232, TUG 1745-14 • 7 specs; Vormsi Island, Hosholm shore (tower locality); Adila Formation, Pirgu Regional Stage; GIT 840-265, GIT 840-266, GIT 878-285 to GIT 878-287, GIT 878-298, GIT 878-305 • 1 spec.; Vohilaid Island; Vohilaid outcrop 8 (8 after B. Stein), Pirgu Regional Stage; GIT 878-149 .</p><p>Type locality and horizon</p><p>Zawidowice by Oleśnica, Poland; erratic boulder, Vormsi–Pirgu regional stages (“Lyckholm Stufe” of Teichert 1930).</p><p>Description</p><p>Nine specimens with mature body chambers are in the Estonian collections (GIT 840-265, -266, GIT 878-149, -285, -286, -287, -298, -305, TUG 899-80, TUG 1445-232, TUG 1745-14) (Fig. 12H). Amongst these specimens’ the conch diameter at the base of the body chamber varies between 18–22 mm (mean = 20.1 mm). At the position of the base of the mature body chamber the conch is slightly curved. In specimen GIT 878-149, the body chamber deviates ca 10° against the adapical part of the conch; it is ca 45 mm long and decreases from 22 mm at its base to a diameter of 19 mm at ca 30 mm from the base, indicating maturity. Adorally, toward the mature aperture, the diameter again increases to 20 mm, forming an irregular constriction with one or two shallower and irregularly spaced annuli. Similar body chamber modifications occur in the other specimens.</p><p>The conchs are annulated with ca three to four annulations in a distance equal to the corresponding conch cross section (mean RCL = 0.28, n = 16). There is no ontogenetic trend of decreasing or increasing relative distance of the annulations (Fig. 18B). The conch surface is poorly preserved in all specimens, but where visible, ca 28–30 shallow longitudinal lirae occur around the circumference.</p><p>The maximum apical angle measured in a juvenile specimen is ca 8° (specimen GIT 840-138). The angle of expansion decreases with increasing conch diameter (Fig. 18A). The septa are equally spaced as the annulations, are invariably positioned within the troughs of the annulations, and like the annulations, are directly transverse. The position of the siphuncle is central or nearly so. In specimen GIT 840-138, the septal foramen is ca 1 mm in diameter where the conch diameter is 10 mm and in specimen GIT 878-149, the septal foramen is 1.5 mm where the conch diameter is 22 mm. The septal necks are short cyrtochoanitic in early growth stages (specimen GIT 840-138, Fig. 11C) and suborthochoanitic in late growth stages (specimen GIT 878-149, Fig. 11B). The shape of the siphuncle accordingly varies from an expanded barrel shape in early growth stages to subtubular in late growth stages.</p><p>Remarks</p><p>Roemerʼs (1861) original description of O. clathrato-annulatum is based on material, which very likely represents multiple taxa of annulated orthocones. The original description emphasized the reticulate pattern (with finer transverse than longitudinal lirae), and the decreasing conch diameter of the mature body chamber as diagnostic characters of this species (Roemer 1861: 58). No explicit information regarding the number of longitudinal lirae was provided by Roemer (1861). The only illustrated specimen has 22 longitudinal lirae in lateral view (suggesting a total of ca 40–45 lirae), and ca three to four annulations in a distance similar to the conch diameter (Roemer 186: pl. 7 fig. 4).</p><p>Roemer (1861: 58) distinguished O. clathrato-annulatum from the similar O. textum-araneum by the position of the siphuncle (central in the former), the adult size (much larger in the latter), and the shape of the mature body chamber (curved in the latter).</p><p>However, Dzik (1984: pl. 35 fig. 4a–c) figured a fragment of a phragmocone as holotype of O. clathrato-annulatum with no traces of the fine reticulate pattern described in the original description, leaving some uncertainty about the ornamentation of this species. Moreover, this specimen has great similarities to specimens described herein under Striatocycloceras hosholmensis sp. nov. The internal characters and details of ornamentation of this specimen, however, remain unknown.</p><p>Teichert (1930), followed Roemerʼs (1861) concept of O. clathrato-annulatum (i.e., reticulate ornamentation, relatively small mature body chamber with decreasing conch diameter), and distinguished two, roughly similar species in the strata of Lyckholm, Estonia: a large-sized Spyroceras textumaraneum and a smaller Spyroceras clathrato-annulatum . A reinvestigation of Roemerʼs (1861) type material is needed to clarify if Teichertʼs (1930) interpretation of O. clathrato-annulatum is consistent with the types or if this species needs a radical reinterpretation (i.e., if S. hosholmensis sp. nov. is a subjective junior synonym of O. clathrato-annulatum and if the species described herein under G. clathratoannulatum represents a new species).</p><p>For the time being, the diagnosis, given herein, follows Teichertʼs (1930) interpretation. Details of the ornamentation of O. clathrato-annulatum, and of the siphuncle and septal necks, which are missing in Roemer (1861) and Teichert (1930), are appended to the diagnosis, based on the new Estonian material.</p><p>Strand (1934) described several specimens from the Late Ordovician “Gastropod Limestone” of Norway under Spyroceras cf. clathrato - annulatum . The Norwegian specimens, ornamented with ca 40 longitudinal lirae, and described under this taxon, probably belong to G. textumaraneum or Gorbyoceras? stumburi (Kröger 2013) (see below). The specimen described by Strand (1934: 21), ornamented with ca 60 longitudinal lirae and an apical angle of 7–8° at conch diameters up to 21 mm, is certainly not a G. clathratoannulatum, because at this size, this species has a nearly tubular conch or is decreasing in diameter, as well as possessing a smaller number of longitudinal lirae. It can probably be synonymized with specimen TUG 939-78, described herein as Palaeodawsonoceras? sp. A.</p></div>	https://treatment.plazi.org/id/932687839651700FFE5CFE42FBC4FB42	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783965F700CFDC8FB76FDC7FC0A.text	93268783965F700CFDC8FB76FDC7FC0A.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Gorbyoceras stumburi (Kroger 2013)	<div><p>Gorbyoceras stumburi (Kröger, 2013)</p><p>Figs 12J, 18</p><p>Dawsonoceras stumburi Kröger, 2013: 32–34, figs 16e, 17b.</p><p>Dawsonoceras sp. – Kröger &amp; Isakar 2006: 157, figs 10e, j, 12h.</p><p>Diagnosis</p><p>Annulated orthocones with angle of expansion of ca 5° and circular cross section; ca five relatively shallow annulations occur in a distance similar to conch diameter; approximately 40 longitudinal lirae occur around shell circumference, more than 10 pronounced transverse striae occur per cycle of annulations; septal necks achoanitic; siphuncle subcentral, fusiform, expanded within chambers. (Adopted from Kröger 2013.)</p><p>Material examined</p><p>ESTONIA • 1 spec.; Vormsi Island, Hosholm shore; Adila Formation, Pirgu Regional Stage; TUG 1745- 47 • 1 spec.; Harilaid; Vormsi – Pirgu regional stages; TUG 939-30 • 1 spec.; Vormsi Island, Saxby shore; Kõrgessaare Formation, Vormsi Regional Stage; TUG 939-21 .</p><p>Type locality and horizon</p><p>Kallholn, Siljan District, Sweden; Boda Limestone, Boda Core Member, late Katian, Ordovician.</p><p>Description</p><p>Specimen TUG 1745-47 is a slightly curved fragment of a mature body chamber with a length of ca 35 mm and a maximum diameter of 20 mm. Approximately five annulations occur in a distance similar to the conch diameter. The surface is ornamented with ca 40 longitudinal lirae around the circumference and fine growth lines. At its base, the fragment has a diameter of 19 mm and a chamber of the phragmocone is preserved with two septa which are 5 mm distant. The septa are located in the troughs of the respective annulations and are directly transverse, parallel to the annulations. The septal foramen is poorly preserved but apparently slightly eccentric in position and located toward the convex side of the conch curvature.</p><p>Specimen TUG 939-30 (Fig. 12J) is a nearly tubular fragment of a body chamber with relatively well-preserved conch surface showing ca 40 longitudinal lirae across the circumference and fine transverse lirae or raised growth lines (ca 10–12 per cycle of annulation). The spacing of the annulation is relatively narrow with 5–6 cycles of annulations per distance similar to the corresponding conch cross section.</p><p>Remarks</p><p>No new data on the internal characters of this species can be added with the Estonian material. The species was originally placed within Dawsonoceras . However, based on the similarity of the known characters from this species with other species of Gorbyoceras and following the more restricted genus diagnosis of Dawsonoceras of Horny (1956), followed herein (see above), a placement within Gorbyoceras is suggested, herein.</p></div>	https://treatment.plazi.org/id/93268783965F700CFDC8FB76FDC7FC0A	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783965C700AFDF9FBAEFBC5FDF6.text	93268783965C700AFDF9FBAEFBC5FDF6.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Gorbyoceras textumaraneum (Roemer 1861)	<div><p>Gorbyoceras textumaraneum (Roemer, 1861)</p><p>Figs 11D, 12D–E, L–M, 18</p><p>Orthoceras textum-araneum Roemer, 1861: 58–59, pl. 7 fig. 3a–b.</p><p>Orthoceras textum-araneum – Rüdiger 1889: 52–53.</p><p>Spyroceras textum-araneum – Teichert 1930: 280, pl. 5 fig. 6.</p><p>Spyroceras cf. clathrato-annulatum – Strand 1934: 21 (partim).</p><p>Spyroceras textum-aranaceum [sic] – Balashov 1953a: 212; 1955: 98–99, pl. 45 fig. 3; 1962b: 108, pl. 48 fig. 1.</p><p>Gorbyoceras textumaraneum – Dzik 1984: 121, text-fig. 49.15, pl. 35 fig. 6. ― Kröger &amp; Isakar 2006: 158–159, figs 8c, 10c–d, 12a–b. ― Pohle et al. 2022: fig. 2.</p><p>Diagnosis</p><p>Slightly compressed orthocones with curved mature body chamber; adult conch diameter ca 40 mm; ornamented with three to four annulations in a distance equal to the corresponding conch diameter; annulations straight or very slightly oblique to the normal of the conch axis and slightly irregularly spaced; fine growth lines, about 15 per annulation; additionally ornamented with fine longitudinal lirae; suture lines in the troughs of the annulations and equally spaced with the annulations; parallel sutures and annulations; siphuncle eccentric in juvenile, subcentral in more adult growth stages; septal foramen approximately one tenth of the diameter. (Compiled from Roemer 1861 and Kröger &amp; Isakar 2006.)</p><p>Material examined</p><p>ESTONIA • 1 spec.; Haapsalu holm; Adila Formation, Pirgu Regional Stage; TUG 1745-238 • 1 spec.; Vormsi Island, Hosholm shore; Adila Formation, Pirgu Regional Stage; TUG 1743-77 238 • 5 specs; Vormsi Island, Hosholm shore (N); Adila Formation, Pirgu Regional Stage; GIT 878-223, GIT 878- 224, GIT 878-282 to GIT 878-284 • 1 spec.; Mõnuste quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 1745-193 • 1 spec.; Paluküla quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 225-968 • 5 specs; Vohilaid Island, Vohilaid shore (E); Adila Formation, Pirgu Regional Stage; GIT 878- 143, GIT 878-299 to GIT 878-301, GIT 878-306 .</p><p>Type locality and horizon</p><p>Zawidowice by Oleśnica, Poland; erratic boulder, Vormsi–Pirgu regional stages (“Lyckholm Stufe” of Teichert 1930).</p><p>Description</p><p>The largest specimen of this species in the Estonian collections is TUG 1745-193 from Mõnuste quarry, Vormsi Regional Stage (Fig. 12L). The specimen is a nearly complete internal mold of a slightly curved body chamber and one chamber of the phragmocone with maximum conch height of 37 mm and conch width 41 mm at the adoral end of the preserved part of the body chamber. The body chamber is ca 100 mm long with conch height ca 32 mm and conch width ca 35 mm at its base, and with eight directly transverse annulations. The five adapical annulations of this specimen are regularly spaced, 10–12 mm apart, with widely rounded troughs and more sharper ridges. The three adoral annulations are less well pronounced and irregularly spaced with distances between 12–16 mm. On the adoralmost part of the specimen, traces of distinct irregularly spaced longitudinal lirae are preserved, which are ca 3–4 mm apart, and which would amount to ca 40 around the entire circumference. The two septa preserved at the adapical end of the specimen are 11 mm apart and are positioned in the mid-troughs of the respective annulation. Traces of the septal foramen and siphuncle are not preserved.</p><p>Seven specimens with adult body chambers are preserved (GIT 878-143, GIT 878-224, GIT 878-223, GIT 878-282, GIT 878-283, TUG 1745-193, TUG 1745-238) with conch heights at their bases ranging from 32–35 mm (mean = 33 mm); all are slightly curved and have in the adoral third, a section with irregularly spaced, less well pronounced, annulations (Fig. 12L–M).</p><p>The internal characters are preserved in GIT 878-299, a slightly curved fragment of a phragmocone with a diameter of 29–32 mm. There, the septal foramen has a diameter of ca 2.8 mm, is eccentric on the convex side of the conch curvature 12 mm from the conch margin at its adapical end. The septal necks are poorly preserved, but apparently suborthochoanitic, and the siphuncle is slightly expanded to nearly tubular in shape (Fig. 11D).</p><p>Remarks</p><p>The information available for this species regarding the number of longitudinal lirae across the circumference is confusing. Roemer (1861: 59) counted 22–24 lirae, but in the original illustration (Roemer 1861: pl. 7 fig. 3) 17–18 lirae are visible in lateral view, suggesting a total of ca 35 lirae. There is no evidence that the number of lirae changed during ontogeny. Therefore, Kröger &amp; Isakar (2006: 158) included number of “approximately 35 irregularly spaced longitudinal ridges” in their species diagnosis of G. textumaraneum .</p><p>In contrast, a photograph of the lectotype of G. textumaraneum in Dzik (1984: pl. 35 fig. 6) supports the 22–24 lirae count of Roemer (1861: pl. 7 fig. 3). The specimens described by Kröger &amp; Isakar (2006) under G. textumaraneum have ca 40 lirae. The only Estonian specimen with surface characters preserved (specimen TUG 1745-193) also has ca 40 longitudinal lirae around the circumference. More well-preserved material is needed to evaluate the diagnostic value of this character (i.e., the number of longitudinal lirae) for G. textumaraneum . Strand (1934: 21) described annulated specimens (with three and a half annulations per length equal to diameter), ornamented with ca 40 longitudinal lirae from the Late Ordovician “Gastropod Limestone” under Spyroceras cf. clathrato-annulatum, which can be synonymized with the material described herein.</p><p>Additionally, growth stages of G. textumaraneum with conch diameters &lt;ca 20 mm are poorly known. The species most conspicuous features are confined to the mature body chamber and a smaller species with similar general conch shape and ornamentation exists ( G. stumburi). Fragments with diameters smaller than the adult diameter of G. stumburi (ca 20 mm) therefore cannot be assigned to either G. stumburi or G. textumaraneum . Five specimens (TUG 1745-275, 1745-300, 1745-301, TUG 1819-85, TUG 1827-61) with an ornamentation of the aspect of G. stumburi and G. textumaraneum and diameters&gt; 20 mm and assigned to Gorbyoceras sp. are included in the measurements to illustrate the morphological variability of the entire cohort (Fig. 18A–B) (see measurements in supplementary data 3).</p></div>	https://treatment.plazi.org/id/93268783965C700AFDF9FBAEFBC5FDF6	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783965A700AFD5CFD81FD8FFB35.text	93268783965A700AFD5CFD81FD8FFB35.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Gorbyoceras undefined-A	<div><p>Gorbyoceras sp. A</p><p>Fig. 12N</p><p>Material examined</p><p>ESTONIA • 1 spec.; Kohila quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 42-417 .</p><p>Description</p><p>The specimen is a ca 75 mm long fragment of a curved body chamber with external sculpture partly preserved. The original diameter was larger than 35 mm. The fragment is annulated with ca 4–5 regularly spaced annulations per distance equal to the corresponding conch diameter. The annulations are relatively shallow. Additionally, the conch is ornamented with numerous fine longitudinal lirae and subordinate transverse growth lines, producing a reticulate pattern. The longitudinal and transverse lirae are ca 1 mm distant.</p><p>Remarks</p><p>The ornamentation of this fragment is similar to other species of Gorbyoceras . Its curved, relatively large body chamber (conch diameter&gt; 35 mm) is similar to G. textumaraneum, from which it differs by its fine reticulate ornamentation. The fragmentary preservation of this specimen does not permit a species level determination.</p></div>	https://treatment.plazi.org/id/93268783965A700AFD5CFD81FD8FFB35	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783965A700AFDA3FB4FFE37F95F.text	93268783965A700AFDA3FB4FFE37F95F.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Isorthoceras Flower 1962	<div><p>Genus Isorthoceras Flower, 1962</p><p>Type species</p><p>Orthoceras sociale Hall in Miller, 1877, from Graf, Iowa, USA, Elgin Member, Maquoketa Formation, latest Katian; by original designation.</p><p>Diagnosis</p><p>Orthoconic longicones with subcircular cross section and subdued ornamentation, smooth or with fine transverse and / or longitudinal lirae; siphuncle subcentral, with barrel-shaped early segments and subcylindrical later segments; septal necks suborthochoanitic to cyrtochoanitic; endosiphuncular annuli grow forward and backward, joining those of adjacent segments to form continuous parietal lining of uniform thickness throughout segments; mural to episeptal cameral deposits. (Compiled from Flower 1962 and Frey 1995.)</p></div>	https://treatment.plazi.org/id/93268783965A700AFDA3FB4FFE37F95F	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783965A7016FDF2F967FBC8FB1C.text	93268783965A7016FDF2F967FBC8FB1C.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Isorthoceras luhai (Stumbur 1956) Kröger 2025	<div><p>Isorthoceras luhai (Stumbur, 1956) comb. nov.</p><p>Figs 19A–C, F, 20–21</p><p>Orthoceras luhai Stumbur, 1956: 179–180, text-fig. 1, pl. 1 figs 2–3, pl. 2 fig. 4, pl. 3 fig. 1. Michelinoceras dnestrovense Balashov, 1975: pl. 2 figs 7–8.</p><p>Isorthoceras dalecarlense Kröger et al., 2011: 45, fig. 9c, g.</p><p>Isorthoceras dalecarlense – Kröger 2013: 58–59, figs 4b, 26.</p><p>Diagnosis</p><p>Smooth, nearly straight Isorthoceras with circular cross section and comparatively low angle of expansion of 6°, chamber distance 0.3 of corresponding cross section, depth of septal curvature ca 0.26 of corresponding cross section; adult size&gt; 35 mm in cross section; siphuncle eccentric in early, subcentral in later growth stages, siphuncular segments slightly expanded within chambers with diameter ca 0.1 of conch cross section; septal necks short, bordering between cyrtochoanitic and suborthochoanitic; in apical parts of siphuncle thin parietal deposits, that ventrally fuse forming irregular endosiphuncular lining in extreme apical part of conch; cameral deposits not known. (From Kröger et al. 2011.)</p><p>Material examined</p><p>ESTONIA • 1 spec.; Haapsalu holm; Adila Formation, Pirgu Regional Stage; TUG 2-359 • 1 spec.; Vormsi Island, Hosholm shore (tower outcrop); Adila Formation, Pirgu Regional Stage; GIT 878-291 • 1 spec.; Jootma ditch; Moe Formation, Pirgu Regional Stage; GIT 426-577 • 1 spec.; Kohila; Kõrgessaare Formation, Vormsi Regional Stage; TUG 939-1 • 1 spec.; Paluküla quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-1108 • 1 spec.; Saksi manor; Kõrgessaare Formation, Vormsi Regional Stage; TUG 1745-215 • 2 specs; Vormsi Island, Saxby shore; Kõrgessaare Formation, Vormsi Regional Stage; TUG 80-474, TUG 895-24 • 4 specs; Vormsi Island, Saxby shore (N); Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-1124, GIT 878-30, GIT 878-45, GIT 878-60 • 1 spec.; same data as for preceding; TUG 1745-222 .</p><p>Type locality and horizon</p><p>Kohila, Estonia; Vormsi Regional Stage.</p><p>Description</p><p>This species was described in detail as I. dalecarlense in Kröger et al. (2011) and Kröger (2013). Here, new data regarding the variability of the angle of expansion, the relative chamber length and the relative siphuncle position can be added – especially for specimens with diameters larger than 20 mm (Figs 20– 21). The data show that the apical angle decreases from a maximum of 8° at conch diameters 16–20 mm (specimen TUG 80-474) to a minimum of 3° at conch diameters 29–32 mm (specimens GIT 426-1108, GIT 878-30) (Fig. 20A). Similarly, the relative chamber length decreases in growth stages greater than 16 mm in diameter, reaching maximum values at ca 16 mm with an RCL of 0.32 (specimen TUG 895- 24) and minimum values of an RCL of less than 0.2 at conch diameters larger than 24 mm (specimens GIT 426-1108, GIT 878-60, GIT 878-291) (Fig. 20B). The position of the siphuncle changes during ontogeny from RSP 0.32 (specimen TUG 2-359) at a conch diameter of 12 mm toward a central position in specimens with diameters larger than 30 mm (specimen GIT 878-30) (Fig. 20C).</p><p>The septal necks are short suborthochoanitic with a siphuncle that appears to be more expanded, barrel-shaped in earlier growth stages and more tubular in later growth stages (Fig. 19A–C, F). Endosiphuncular and cameral deposits are absent in the specimens which were cut and polished at median position. These have diameters larger than ca 15 mm.</p><p>Remarks</p><p>The species was established based on a single, poorly preserved specimen (holotype: GIT 939-1, Fig. 19C). With the nine specimens, described herein, the range of variation of this species becomes apparent (measurements are available in supplementary data 3). The new data reveal that the type-material of I. dalecarlense Kröger et. al., 2011 is, at comparable growth stages, well within the known range of variation of the shell features of I. luhai (Fig. 20). Therefore, I. dalecarlense must be interpreted as subjective junior synonym of I. luhai . The same can be said for Michelinoceras dnestrovense Balashov, 1975 from late Katian strata of Podolia, Ukraine (see Fig. 20).</p><p>The Estonian fragments are on average larger in diameter than the types of I. dalecarlense from the Glisstjärn Formation, Hirnantian, Sweden (Kröger et al. 2011). Together with the Swedish material described as I. dalacarlense from the Boda Limestone, Sweden, this now permits an evaluation of the ontogenetic changes of the angle of expansion, of the RCL, and the RSP from juvenile stages to near maturity (Figs 20–21).</p><p>As a result, divergent trajectories in early growth stages for the angle of expansion between the samples of I. dalecarlense from the Glisstjärn, and from that of the slightly older Boda Formation, Sweden (see Kröger 2013: fig. 26) are evident. The specimens assigned to D. dalecarlense from the Boda Formation initially have a low angle of expansion, which increases toward a diameter of ca 15 mm. The Glisstjärn material, in contrast, shows a continuously decreasing angle of expansion throughout ontogeny (Fig. 21) (Note: in Kröger 2013: fig. 26, correctly the grey dots represent the type-material and the dots with black circles the Boda material, compare Kröger et al. 2011: fig. 10). This difference could be interpreted as an intraspecific variability within I. luhai or, alternatively as evidence for the presence of two different species, one in the Boda Formation and another in the Glisstjärn Formation. Additional specimens of the smaller size fraction from Estonia are needed to test if the Estonian I. luhai follows the early ontogeny trajectory of the I. dalecarlense - type material from the Glisstjärn Formation or that of the Boda Formation. The latter case would open the possibility to distinguish between I. luhai with a low juvenile angle of expansion and I. dalecalense with a high juvenile angle of expansion. Until more material is known, the most parsimonious solution to the problem is followed, which is to synonymize the three samples under I. luhai, which has priority.</p><p>Comparison</p><p>Isorthoceras luhai differs from the co-occurring I. saaremense (Balashov, 1959) in having a smaller angle of expansion at comparable growth stages (Fig. 20A) and in having a less eccentric siphuncle position (mean RSP is 0.4, compared with 0.3 in in I. saaremense, Fig. 20C).</p></div>	https://treatment.plazi.org/id/93268783965A7016FDF2F967FBC8FB1C	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396467017FE27FA98FBF7F903.text	9326878396467017FE27FA98FBF7F903.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Isorthoceras saaremense (Balashov 1959) Kröger 2025	<div><p>Isorthoceras saaremense (Balashov, 1959) comb. nov.</p><p>Figs 15D, 19D, G</p><p>Hedstroemoceras saaremense Balashov, 1959: 42, pl. 5 fig. 11.</p><p>Hedstroemoceras saaremense – Balashov &amp; Zhuravlyeva 1962: pl. 13 fig. 2; 1974: pl. 13 fig. 2.</p><p>Emended diagnosis</p><p>Isorthoceras with circular conch cross section; smooth shell surface; weakly curved growth axis with siphuncle slightly eccentric (RSP = 0.29) on concave side of curvature; angle of expansion of up to ca 12°; mature body chamber with maximum diameter more than 40 mm; siphuncular segments pyriform to fusiform; with weakly developed endosiphuncular deposits; septal necks short, suborthochoanitic to orthochoanitic.</p><p>Material examined</p><p>ESTONIA • 1 spec.; Kersleti quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 1745-305 • 1 spec.; Paluküla quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-570 • 1 spec.; Paope quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 939-2 • 1 spec.; Salutaguse quarry; Moe Formation, Pirgu Regional Stage; GIT 878-138 • 4 specs; Vormsi Island, Saxby shore; Kõrgessaare Formation, Vormsi Regional Stage; TUG 1743-4, TUG 1745-223, TUG 1745-246, TUG 1745-259 • 4 specs; Vormsi Island, Saxby shore (N); Kõrgessaare Formation, Vormsi Regional Stage; GIT 426- 1133, GIT 878-40, GIT 878-41, GIT 878-20 • 1 spec.; Sutlema quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-128 .</p><p>Type locality and horizon</p><p>Tapa, Estonia; Vormsi–Pirgu regional stages.</p><p>Description</p><p>Specimen GIT 878-41 is a 155 mm long fragment of part of a body chamber and phragmocone with a diameter of 19–39 mm (angle of expansion = 7.4°). The preserved part of the body chamber is 61 mm long with a conch diameter of 33 mm at its base. The conch cross section is circular or slightly compressed. The conch is slightly curved. Where preserved, the conch surface is smooth. The sutures are directly transverse and 5.5 mm distant at a corresponding conch diameter of 32 mm and 4.5 mm at a conch diameter of 24 mm. The septal foramen is located 10 mm from the margin of the conch at the convex side of the conch curvature, and has a diameter of 2.3 mm where the conch height is 31 mm.</p><p>The complete set of measurements available reveals a decreasing angle of expansion from 12° at corresponding conch diameters of ca 15 mm toward 9°–4° in more mature specimens (Fig. 20A). The relative cameral length decreases.from ca 0.25 to less than 0.15 (mean RCL = 0.21, n = 10).</p><p>The details of the internal characters are preserved in specimens GIT 878-40, GIT 878-20, TUG 939-2, TUG 1745-246, 1745-259, and TUG 1745-305, These represent fragments of the phragmocone with diameters between 19–37 mm (Fig. 19D, G). In all specimens the shape of the siphuncle is slightly expanded, barrel-shaped with greatest widths at ca mid-length of the siphuncular segments, and the septal necks are short orthochoanitic to suborthochoanitic. The position of the siphuncle varies between RSP 0.2–0.3 with no apparent ontogenetic trend (mean RSP = 0.3, n= 7).</p><p>Remarks</p><p>This species was originally classified within the Middle Ordovician genus Hedstroemoceras Foerste, 1930a, without explicit justification, probably based on its eccentric siphuncle. It has been originally described from a single poorly preserved small fragment of a phragmocone. The outer shell in the holotype is not preserved. The specimen can be identified, based on its siphuncular position and septal neck features, as an Isorthoceras . It has an eccentric siphuncle position (RSP = 0.27) at a conch diameter of 44 mm, and an apparently a very low angle of expansion. In the context of the additional material, the holotype can be interpreted as an adoral fragment of a phragmocone of a near mature specimen with a low angle of expansion, and, in contrast to I. luhai, an eccentric siphuncle during late ontogeny.</p><p>Comparison</p><p>This species is in almost all aspects like I. wahlenbergi from the Boda Limestone, Late Katian, Sweden. It differs from the latter in its larger size. Isorthoceras wahlenbergi reaches an adult size of ca 30 mm, which is documented in numerous specimen (Niko 2008; Kröger 2013: fig. 26). Immature specimens of I. saaremense can be distinguished from I. wahlenbergi by their more central siphuncular position: the mean RSP is 0.22 in I. wahlenbergi (Kröger 2013: 66), it is 0.29 in I. saaremense .</p></div>	https://treatment.plazi.org/id/9326878396467017FE27FA98FBF7F903	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396477014FD5DF8B4FBCEFD1B.text	9326878396477014FD5DF8B4FBCEFD1B.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Isorthoceras undefined-A	<div><p>Isorthoceras sp. A</p><p>Fig. 12A</p><p>Material examined</p><p>ESTONIA • 1 spec.; Sutlema quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-128 .</p><p>Description</p><p>The specimen is a ca 45 mm long fragment of parts of a mature body chamber and three phragmocone chambers with a circular conch cross section. The maximum diameter of the specimen is 16 mm at ca mid-length of the body chamber. The body chamber is at least 34 mm long and at its base 15 mm in diameter. At ca 15 mm from its base, the body chamber has a wide, shallow constriction occurs. The three preserved chambers of the phragmocone decrease in length from 4 mm to 3.2 mm, to 2 mm in adoral direction. The septal foramen is well-preserved at 3.7 mm from the conch margin, where the conch cross section is 15 mm in diameter (RSP = 0.27), and it has a diameter of 1.2 mm. The conch surface is apparently smooth, although fine details of the ornamentation are not preserved.</p><p>Remarks</p><p>This specimen can be related to I. heroyense (Strand, 1934), and I. angelini Kröger, 2013, with respect to the mature conch size, position of the siphuncle and general conch shape. However, because the nature of the conch surface is uncertain, a species level determination is impossible.</p></div>	https://treatment.plazi.org/id/9326878396477014FD5DF8B4FBCEFD1B	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396447014FD5CFC9DFCFEFA0A.text	9326878396447014FD5CFC9DFCFEFA0A.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Isorthoceras undefined-B	<div><p>Isorthoceras sp. B</p><p>Fig. 12B</p><p>Material examined</p><p>ESTONIA • 1 spec.; Moe trench; Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-116 .</p><p>Description</p><p>Specimen GIT 878-116 is a ca 12 mm long internal mold of parts of a mature body chamber and three phragmocone chambers with a circular conch cross section. The maximum diameter of the specimen is 10 mm at its adoral end. At the base of the body chamber the diameter is 9.8 mm and the adapicalmost chamber has a diameter of 9.6 mm (angle of expansion 2.5°). The three preserved chambers of the phragmocone decrease in length from 2.4 mm to 1.5 mm, to 0.5 mm adorally. The septal foramen is well preserved at 1.7 mm from the conch margin, where the conch cross section is 9.6 mm in diameter (RSP = 0.18), with a diameter of 1.1 mm (RSH = 0.11). The conch surface is apparently smooth, although fine details of the ornamentation are not preserved.</p><p>Remarks</p><p>This specimen can be related to I. junceum (Hall, 1847) with respect to the mature conch size, position of the siphuncle, and general conch shape. However, because the crucial details of the conch surface are not preserved, a species level determination is not possible.</p></div>	https://treatment.plazi.org/id/9326878396447014FD5CFC9DFCFEFA0A	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396447015FD5CF9AEFABFFE33.text	9326878396447015FD5CF9AEFABFFE33.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Isorthoceras undefined-C	<div><p>Isorthoceras sp. C</p><p>Fig. 12F</p><p>Material examined</p><p>ESTONIA • 1 spec.; Vormsi Island, Saxby shore; Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-49 .</p><p>Description</p><p>This specimen is a fragment of a body chamber and four chambers of the phragmocone with a nearly tubular circular conch with a diameter of 9.2–9.5 mm and an angle of expansion of ca 1°. The preserved part of the body chamber is 16 mm long, the septa are ca 1.8 mm apart, respectively (RCL = 0.19), and the septal foramen is eccentric with an RSP of 0.28. The septa are directly transverse. The conch surface is not preserved.</p><p>Remarks</p><p>This specimen can be compared with Isorthoceras sp. B, but its lower angle of expansion at smaller conch diameters indicates an even smaller adult size (ca 10 mm) of this species. The lack of external shell prohibits any species level determination. However, based on the small adult size, conch shape and siphuncular position the species can be related to I. junceum . Another small species known from Late Ordovician strata of Sweden, I. curvilineatum Kröger, 2013, differs in having a central siphuncle.</p></div>	https://treatment.plazi.org/id/9326878396447015FD5CF9AEFABFFE33	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396457015FD5BFE43FC13FA19.text	9326878396457015FD5BFE43FC13FA19.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Isorthoceras undefined-D	<div><p>Isorthoceras sp. D</p><p>Fig. 11I</p><p>Material examined</p><p>ESTONIA • 2 specs; Moe trench; Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-114, GIT 878-125 • 1 spec.; Paluküla quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-433 • 2 specs; Vormsi Island, Saxby shore; Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-44, GIT 878-83 • 2 specs; same data as for preceding; TUG 939-3, TUG 939-4 .</p><p>Description</p><p>Specimen GIT 878-114 (Fig. 11I) is a fragment of a body chamber and one chamber of the phragmocone. The body chamber is slightly deformed and does not permit measurement of the angle of expansion. The conch cross section at the base of the body chamber is circular with a diameter of 10 mm. The preserved two septa are 1.8 mm apart (RCL = 0.18) and the septal foramen is nearly centrally positioned (RSP = 0.46) with a diameter of ca 1 mm. The outer shell is not preserved. Specimen TUG 939-4 is a fragment of a body chamber and seven chambers of the phragmocone with a circular conch cross section. The septal distance varies between 2.5–3.5 mm (RCL = 0.23–0.39) and is most distant at smaller diameters (9 mm) and decreases toward the base of the body chamber at the base of the body chamber 11 mm. The angle of expansion of the specimen is ca 3°. The siphuncle is nearly central (RSP = 0.45), its shape is nearly tubular, and the septal necks are very short suborthochoanitic to orthochoanitic. The largest specimen is a fragment of a 28 mm long body chamber with a maximum diameter of ca 13 mm (GIT 878-83).</p><p>Remarks</p><p>The adult size of this species is indicated by mature septal crowding occurring in specimens TUG 939- 4, and GIT 878-114 at conch diameters of ca 10–11 mm. The maximum adult diameter at the aperture was probably not much more than 13 mm. These specimens are assigned to Isorthoceras based on their similarity with other small orthocerids known from the Late Ordovician of Baltoscandia, and because of their short suborthochoanitic septal necks. They differ from I. sp. E in having a central siphuncle. Better preserved material is needed for a species level determination.</p></div>	https://treatment.plazi.org/id/9326878396457015FD5BFE43FC13FA19	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396457012FD5DF999FD93FE1B.text	9326878396457012FD5DF999FD93FE1B.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Isorthoceras undefined-E	<div><p>Isorthoceras sp. E</p><p>Fig. 19E</p><p>Material examined</p><p>ESTONIA • 1 spec.; Vormsi Island, Saxby shore, Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-1132 .</p><p>Description</p><p>The specimen is a 110 mm long, 27–32 mm high fragment of a phragmocone (angle of expansion ca 4°) with 16 chambers preserved (RCL 0.21–0.31), and with a circular cross section. The outer shell is not preserved. The siphuncle is eccentric (RSP = 0.31) and, where preserved, with a straight, tubular connecting ring. The septal necks are short (ca 0.8 mm long) orthochoanitic-suborthochoanitic and shallow endosiphuncular annuli occur.</p><p>Remarks</p><p>This specimen is unique among the larger Isorthoceras fragments in having a combination of relatively low angle of expansion (comparable to I. luhai at similar conch heights) and a relatively eccentric siphuncle position (comparable to I. saaremense at similar conch heights). Additionally, the siphuncle is more tubular than compared to the other species of Isorthoceras known from Estonia, and shallow endosiphuncular deposits occur. More material is needed with external characters preserved to allow for a species level determination.</p></div>	https://treatment.plazi.org/id/9326878396457012FD5DF999FD93FE1B	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396427012FDB5FCC6FE9EFAA3.text	9326878396427012FDB5FCC6FE9EFAA3.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Charactoceras Foerste 1924	<div><p>Genus Charactoceras Foerste, 1924</p><p>Type species</p><p>Trochoceras (?) baeri Meek &amp; Worthen, 1866, Richmond, Indiana, USA, Whitewater Formation, late Katian, Ordovician; by original designation.</p><p>Diagnosis</p><p>Closely coiled, rapidly expanding conchs with dorsally impressed whorl cross section, with flattened venter and rounded sides that converge towards the dorsum; sutures essentially straight laterally but forming broad ventral and dorsal lobes; surface with transverse growth lines that form distinct hyponomic sinus on venter, and transverse ribs in early stages only; siphuncle between center and venter, with cyrtochoanitic septal necks, empty; segments expanding slightly within camerae.” (Adopted from Sweet 1964a.)</p></div>	https://treatment.plazi.org/id/9326878396427012FDB5FCC6FE9EFAA3	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396427012FDDCFD9DFAD1FCF3.text	9326878396427012FDDCFD9DFAD1FCF3.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Multiceratoidea Mutvei 2013	<div><p>Subclass Multiceratoidea Mutvei, 2013</p><p>Remarks</p><p>Herein, the classification of Pohle et al. (2022) is followed. The order Oncocerida Flower in Flower &amp; Kummel, 1950 is rejected (but see supplementary data 1, and remarks in Methodology section), because it represents a paraphyletic group (Pohle et al. 2022). Below, families, previously classified within the Barrandeocerida or Oncocerida are listed alphabetically, without assigning them to an existing order.</p></div>	https://treatment.plazi.org/id/9326878396427012FDDCFD9DFAD1FCF3	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396427013FDC1FAD4FC1EF91D.text	9326878396427013FDC1FAD4FC1EF91D.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Charactoceras estonicum Strand 1934	<div><p>Charactoceras estonicum Strand, 1934</p><p>Fig. 22A</p><p>Charactoceras estonicum Strand, 1934: 28–29, pl. 2 fig. 5, pl. 7 fig. 1.</p><p>Charactoceras estonicum – Balashov 1953b: 266, pl. 11 figs 1–2; 1962c: pl. 7 fig. 1. ― Stumbur 1962: 136. ― Dzik 1984: 44, 154, text-figs 12.30, 59.5.</p><p>Diagnosis</p><p>Charactoceras with smooth, rapidly expanding conch (WER ca 3–4), and adult diameter of ca 140 mm; whorl cross section with rounded venter and rounded umbilical margins, and with deeply impressed dorsal furrow, moderately compressed with WWI ca 1.1–1.3 with greatest width in the dorsal half; sutures with broad and shallow ventral lobes and ventro-lateral saddles; siphuncle close to ventral conch margin. (Adopted from Strand 1934.)</p><p>Material examined</p><p>ESTONIA • 2 specs; Vormsi Island, Hosholm shore; Adila Formation, Pirgu Regional Stage; TUG 939- 68, TUG 1745-274 • 5 specs; Vormsi Island, Hosholm shore (tower locality); Adila Formation, Pirgu Regional Stage; GIT 878-216 to GIT 878-220 • 2 specs; Vohilaid Island, Vohilaid shore (E); Adila Formation, Pirgu Regional Stage; GIT 878-198, GIT 878-229 .</p><p>Type locality and horizon</p><p>Piirsalu, Estonia; Moe Formation, Pirgu Regional Stage.</p><p>Description</p><p>The species has been described in detail by Strand (1934). Additional measurements, taken from the Estonian specimens, contribute to the knowledge on its variability in WWI and WER. The measurements show that WER and WWI are nearly constant throughout different growth stages, with a mean WWI = 2.16 (1 st quartile 1.14–3 rd quartile 1.26, n = 10,) and a mean WER = 3.44 (1 st quartile 3.27–3 rd quartile 3.45, n = 5). Also, the shape of the whorl cross section does not change significantly at different growth stages with rounded venter and flanks and greatest width located in the dorsal half of the whorl.</p><p>The most complete specimen in the collection (apart from the holotype TUG 939-68, which has been described in detail by Strand 1934 and Balashov 1953b), is GIT 878-229. This specimen is a fragment of a phragmocone consisting of two whorls, and has a maximum diameter of 72 mm. The preceding whorl has a diameter of 40 mm (WER = 3.24). At a conch diameter of 44 mm, the next whorl has a diameter of 24 mm (WER = 3.36). The WWI is 1.13 at a conch width of 36 mm, 1.20 at a conch width of 24 mm, and 1.1 at a conch width of 11 mm. The septa are 8 mm apart at the venter where the whorl height is 32 mm. The septal foramen is located 3 mm from the ventral conch margin and has a diameter of 3 mm where the conch height is 28 mm (RSH = 0.11, RSP = 0.12).</p><p>Remarks</p><p>The diagnosis is adopted from Strand (1934: 28). Here, the WER and WWI are used to describe the relative conch dimensions and are included in the diagnosis; their values are based on the type specimen.</p><p>Comparison</p><p>Charactoceras estonicum is apart from the Laurentian palaeocontinent known only from Baltica (see Foerste 1926, 1928b, 1935 a, 1935b; Troedsson 1926; Strand 1934; Wilson 1961; Nelson 1963; Frye 1982). Species of Charactoceras are differentiated by whorl cross section shape, ornamentation, and expansion rate. All four species of Charactoceras described by Frye (1982) from the Boda Limestone, late Katian, Sweden, differ in being annulated.</p><p>Charactoceras estonicum is one of the species of Charactoceras with a smooth, non-annulated shell. Among those smooth species, C. laddi Foerste, 1935a, C. manitobaense Nelson, 1963 differ in having a flattened venter, and C. eximium (Sweet &amp; Miller, 1957) and C. triangulum Frye, 1982 differ in having a trapezoidal whorl cross section. An elliptically depressed whorl cross, but with smaller WWI than in C. estonicum, have: C. baeri (WWI = 1.4–1.5, Foerste 1924), C. hercules (Billings, 1857) (WWI = 1.8 at whorl height 53 mm, Nelson 1963: 102), C. normale Wilson, 1961 (WWI = 3.6 at whorl height of 18 mm, Wilson 1961), and C. warranae Nelson, 1963 (WWI = 2 at whorl height of 45 mm). The two species which are most similar to C. estonicum with respect to whorl cross section and ornamentation are C. rotundum Troedsson, 1926 and C. schucherti Foerste, 1928b; they differ in having a smaller expansion rate ( C. rotundum: WER = 2.3 at conch diameter 107 mm, Troedsson 1926), and ( C. schucherti: WER = 2.5 at conch diameter of 47 mm, Foerste 1928b), respectively.</p></div>	https://treatment.plazi.org/id/9326878396427013FDC1FAD4FC1EF91D	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396437011FD50F8A5FB27FC4C.text	9326878396437011FD50F8A5FB27FC4C.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Charactoceras undefined-A Strand 1934	<div><p>Charactoceras sp. A</p><p>Fig. 22C, E</p><p>Material examined</p><p>ESTONIA • 1 spec.; Vormsi Island, Hosholm shore; Adila Formation, Pirgu Regional Stage; GIT 878- 215 .</p><p>Description</p><p>The specimen is a fragment of a nearly complete body chamber and one chamber of the phragmocone with a wide, reniform whorl cross section; it is 36 mm high at the aperture and 57 mm wide. At the base of the body chamber, it measures 24 mm in height and 41 mm in width. The body chamber measures ca 90–100° in length. Throughout its entire length, the greatest width of the whorl is reached between mid-flank and dorsum. On the broadly rounded ventral side, a distinct, broad, U-shaped hyponomic sinus is preserved, which has a width of 35 mm and a depth of 20 mm. Around the aperture patches of the outer shell remain, these are smooth, with distinct narrowly and irregularly spaced growth lines.</p><p>The two septa at the base of the body chamber are 6 mm distant, and a septal foramen located a few millimeters from the venter is apparent, but is not well enough preserved to measure.</p><p>Remarks</p><p>This single fragment does not permit species level determination. The position of the siphuncle and the shape of the body chamber, and its aperture show, however, that this specimen is a fragment of a Charactoceras . Its relatively large WWI of 1.71 (see Fig. 22E) distinguishes the specimen from C. estonicum and suggests a comparison with C. hercules (Billings, 1857) from late Katian strata of Anticosti Island, Quebec (e.g., Foerste 1928c). However, with the available material a detailed comparison is impossible as the more apical parts of the phragmocone are not known.</p></div>	https://treatment.plazi.org/id/9326878396437011FD50F8A5FB27FC4C	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396417011FD50FC68FD50F874.text	9326878396417011FD50FC68FD50F874.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Charactoceras undefined-B Strand 1934	<div><p>Charactoceras sp. B</p><p>Fig. 22D</p><p>Material examined</p><p>ESTONIA • 1 spec.; Vormsi Island, Hosholm shore; Adila Formation, Pirgu Regional Stage; GIT 878- 222 .</p><p>Description</p><p>The specimen is a fragment of a complete body chamber and an additional 14 chambers of the phragmocone. The body chamber is ca 90° long with an unconstricted aperture with a wide U-shaped hyponomic sinus. The total fragment has a conch diameter of 113 mm, and the diameter of the preceding whorl is 83 mm. At its base, the width of the body chamber is 48 mm and the height 39 mm (CHI = 0.81), at the aperture it measures 60 mm in width and 45 mm in height (CHI = 0.75). The septal distance at the base of the body chamber is 6 mm at the venter. There is no sign of mature septal crowding. The sutures run straight and transverse over flanks and venter. At a position where the whorl height is 33 mm, the septal foramen of the siphuncle is ca 2.5 mm in diameter and is located ca 6 mm from the ventral conch margin (RSP = 0.20).</p><p>Remarks</p><p>The fragment does not permit species level determination because the more juvenile growth stages are not preserved. These are critical for species determination because many species of Charactoceras are differentiated by the extent of the annulation of the early growth stages. The WER of 1.85 of this specimen is lower than that of comparable growth stages of the type of C. estonicum (WER&gt;3.5, compare Fig. 22A, D) and of other known species of Charactoceras . The species of Charactoceras with lowest known expansion rate is C. rotundum (WER: 1.9–2.4) from late Katian Strata of northern Greenland (Troedsson 1926). However, this latter species differs in having a siphuncle that is located more distantly from the ventral conch margin.</p></div>	https://treatment.plazi.org/id/9326878396417011FD50FC68FD50F874	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783964E701EFD53FEB0FB18FC36.text	93268783964E701EFD53FEB0FB18FC36.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Charactoceras undefined Foerste 1924	<div><p>Charactoceras? sp.</p><p>Fig. 22B</p><p>Material examined</p><p>ESTONIA • 1 spec.; Paope quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 1006-13 .</p><p>Description</p><p>The specimen is a ca 120° long fragment of a body chamber with a broad elliptical whorl cross section. The dorsal part of the whorl is not preserved. The fragment has a shallow annulations, which run nearly directly transverse over the umbilical margin, ca 19–20 annulations occur per volution. A shallow U-shaped hyponomic sinus is apparent both from faint growth lines preserved on the mold and the shape of the annulations. The preserved part of the conch has a maximum diameter of 52 mm, and the diameter of the preceding whorl is 33 mm (WER = 2.48); at its adoral end the whorl width is 18 mm and the corresponding whorl height is 16 mm (WWI = 1.13).</p><p>Remarks</p><p>The conch shape and ornamentation of this fragmentary specimen is similar to annulated species of Charactoceras, such as C. kallholnense Frye, 1982 or C. suecicum Frye, 1982, However, the siphuncle including the septal foramen are not preserved, making a genus determination uncertain, and the fragmentary character of this specimen does not permit species level determination.</p></div>	https://treatment.plazi.org/id/93268783964E701EFD53FEB0FB18FC36	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783964E701EFD9CFC42FB3BF92E.text	93268783964E701EFD9CFC42FB3BF92E.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Saxbyoceras Kröger 2025	<div><p>Genus Saxbyoceras gen. nov.</p><p>urn:lsid:zoobank.org:act: F9537354-5080-41CB-9ADF-D443823ECEAD</p><p>Type species</p><p>Saxbyoceras kingpooli gen. et sp. nov., from Saxby shore, Kõrgessaare Formation, Vormsi Island, Estonia; Vormsi Regional Stage.</p><p>Diagnosis</p><p>Slightly endogastrically curved brevicone with smooth (or nearly so) conch surface; conch cross section circular or slightly compressed; mature body chamber slightly curved, not (or only very slightly) constricted; sutures are nearly straight and directly transverse; siphuncle eccentrically positioned toward the concave side of the conch with widely expanded segments; septal necks very short or achoanitic; endosiphuncular or cameral deposits not known.</p><p>Etymology</p><p>From Saxby, Vormsi Island, Estonia, the type locality of the type species of this genus.</p><p>Remarks</p><p>The new genus is best compared with Siljanoceras Kröger, 2013, from which it differs in having a much smaller angle of expansion (33° in Siljanoceras) and an endogastrically curved conch.</p></div>	https://treatment.plazi.org/id/93268783964E701EFD9CFC42FB3BF92E	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783964E701CFDC6F94AFC44FAC7.text	93268783964E701CFDC6F94AFC44FAC7.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Saxbyoceras kingpooli Kröger 2025	<div><p>Saxbyoceras kingpooli gen. et sp. nov.</p><p>urn:lsid:zoobank.org:act: 569E3891-BA40-49E8-A7BA-C29851D45C19</p><p>Fig. 23A–B</p><p>Diagnosis</p><p>Same as for genus, by monotypy.</p><p>Etymology</p><p>Refers to Kingpool, the tallest of the three figures in Eno Raud’s (1928–1996) children-book series “Naksitrallid”.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Vormsi Island, Saxby shore, Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-25.</p><p>Paratype</p><p>ESTONIA • 1 spec.; same data as for holotype; TUG 1745-245 .</p><p>Description</p><p>The holotype is a fragment of a slightly endogastrically curved conch consisting of a phragmocone and a mature body chamber. The external shell is partially preserved (Fig. 23A). The conch surface appears smooth but possesses faint narrowly spaced growth lines. In lateral view the body chamber is slightly curved with a straight margin on the prosiphuncular side and a convex margin on the antisphuncular side. It has a height of 78 mm at its base, and 89 mm at its aperture, and a maximum length of 48 mm. The peristome is too fragmentarily preserved to describe its complete outline but a shallow hyponomic sinus is visible on the prosiphuncular side. A faint ca 10 mm wide constriction occurs a few millimeters from the apertural conch margin.</p><p>The phragmocone expands from a height of 65 mm to 78 mm at a length of 41 mm (angle of expansion 18°). At a conch height of 65 mm, a conch width of ca 60 mm can be estimated (CHI = 1.1). The sutures are nearly straight transverse or with a shallow lateral lobe and are 10 mm apart where the conch height is 70 mm (RCL = 0.14). The septal foramen has a diameter of 12 mm and is located ca 17 mm from the concave conch margin where the conch height is ca 60 mm (RSH = 0.20, RSP = 0.35). The connecting ring is thick, the septal necks are short recumbent or achoanitic and no endosiphuncular deposits occur.</p><p>The second specimen is preserved only as two isolated phragmocone chambers with a conch height of 63–70 mm and a septal distance of 12 mm and 10 mm, respectively (RCL: 0.14–0.19). The sutures are directly transverse. The depth of the curvature of the septa is 14 mm where the conch height is 63 mm. The septal foramen is located in a distance of 20 mm from the conch margin with a diameter of 7 mm where the conch height is 63 mm (RSH = 0.11, RSP = 0.36). At a conch height of ca 60 mm, the siphuncular segments are expanded into the chambers with a rounded, convex shape in longitudinal section and with a maximum diameter of 11 mm where the chamber length is 8 mm (RSS = 1.38) and where the septal foramen is 3 mm. The segments have narrow circular adnate areas on the adoral and adapical surfaces of the septa (ca 2 mm wide). The connecting ring is thick, the septal necks are short recumbent or achoanitic and no endosiphuncular deposits occur.</p><p>Remarks</p><p>The specimens described above superficially, and with respect of the position and size of the septal foramen, are similar to specimens described by Eichwald (1860) under Orthoceras declive Eichwald, 1860 . However, because this species apparently combines type material of different taxa from the Middle Ordovician (collected in Tallinn) and from Katian strata (collected in Lyckholm) (Eichwald 1860: 1206–1207) the species name cannot be used until the original material is revised.</p><p>Cyrtoceras substriatum Eichwald, 1860, collected from Hohenholm (= Kõrgessaare; Hiiumaa) is probably related to S. kingpooli sp. nov., because of its similar conch shape and nearly central siphuncle (compare Teichert 1930: 271) but differs in having a transverse ornamentation.</p><p>Another species, which is possibly related to S. kingpooli sp. nov. is Faberoceras demshinense Balashov, 1975 from late Katian strata (Molodovskii horizon) of Podolia, Ukraine, which is a cyrtocone with a nearly central, widely expanded siphuncle. This species differs from S. kingpooli in having a more strongly curved conch and a transversely annulated ornamentation.</p></div>	https://treatment.plazi.org/id/93268783964E701CFDC6F94AFC44FAC7	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783964C701CFDBAFA33FDF3F88A.text	93268783964C701CFDBAFA33FDF3F88A.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Danoceras Troedsson 1926	<div><p>Genus Danoceras Troedsson, 1926</p><p>Type species</p><p>Danoceras ravni Troedsson, 1926, Cape Calhoun, northern Greenland, Cape Calhoun series, Late Ordovician; by original designation.</p><p>Diagnosis</p><p>Slender diestoceratids with straight or slightly curved shell, and compressed conch cross section with narrow venter and / or dorsum; mature body chamber with widest height and width near its base, with simple constriction close to mature aperture, with apertural widening and shallow hyponomic sinus; siphuncle positioned near conch margin, cyrtochoanitic; necks recumbent, segments elongate, subtrapezoidal in longitudinal section; thin annulosiphonate deposits with distinctive irregular linear processes, which extend adapically and adorally without fusing from segment to segment. (Compiled from Strand 1934, and Sweet 1964b.)</p></div>	https://treatment.plazi.org/id/93268783964C701CFDBAFA33FDF3F88A	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783964D701DFD96FEB1FEEFFA93.text	93268783964D701DFD96FEB1FEEFFA93.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Danoceras breve Strand 1934	<div><p>Danoceras breve Strand, 1934</p><p>Fig. 24B</p><p>Danoceras breve Strand, 1934: 81–82, pl. 11 fig. 6, pl. 13 fig. 1.</p><p>Danoceras breve – Flower 1946: 420. ― Dzik 1984: 67, text-fig. 18.11.</p><p>Diagnosis</p><p>Danoceras with compressed elliptical to oval conch cross section (CHI = 1.3–1.4); mature body chamber with maximum conch height near its base with height of ca 42 mm; apical angle of the phragmocone ca 25°; conch surface, with distinct constriction near peristome and amphora-like apertural opening.</p><p>Material examined</p><p>ESTONIA • 1 spec.; Haapsalu holm; Adila Formation, Pirgu Regional Stage; GIT 426-988 .</p><p>Type locality and horizon</p><p>Vestre Svartøy, Ringerike, Norway; Bønsnes Formation, late Katian.</p><p>Description</p><p>The specimen is a slightly deformed fragment of a phragmocone and the mature body chamber. The maximum conch height of the specimen (41 mm) is at the base of the body chamber. There, the conch width is 30 mm (CHI = 1.37). The preserved part of the body chamber is 27 mm long.</p><p>The phragmocone increases in conch height from 23 mm to 40 mm at a length of 38 mm (angle of expansion 25°). At the adoral end of the phragmocone, the chamber length is 6 mm (RCL = 0.15). Traces of a weak longitudinal striation are preserved on the surface of the internal cast of the phragmocone. The conch surface is not preserved. The conch is very slightly curved with a thin (ca 3 mm in diameter) siphuncle preserved near the conch margin at the convex side of the conch curvature.</p><p>Remarks</p><p>This specimen is very similar in dimensions and conch shape to the types of Danoceras breve and although details of the siphuncle are not examined, the thin marginal siphuncle is indicative of a species of Danoceras .</p></div>	https://treatment.plazi.org/id/93268783964D701DFD96FEB1FEEFFA93	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783964D701BFD9EFA24FD00FAC7.text	93268783964D701BFD9EFA24FD00FAC7.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Danoceras oviforme Kröger 2025	<div><p>Danoceras oviforme sp. nov.</p><p>urn:lsid:zoobank.org:act: 8DCABC85-83A4-4DAA-9B32-91D58875FB3F</p><p>Fig. 24A, C</p><p>Diagnosis</p><p>Danoceras with compressed oval conch-cross section (CHI = 1.2); mature body chamber with maximum conch height near its base with height of ca 36 mm and height to length ratio of ca 0.9; maximum conch heigh near adoral end of mature phragmocone.</p><p>Etymology</p><p>Refers to the egg-like conch form of mature specimens.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Moe trench, Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-108. Paratypes</p><p>ESTONIA • 1 spec.; Vormsi Island, Hosholm shore; Adila Formation, Pirgu Regional Stage; TUG 1745- 276 • 1 spec.; Piirsalu quarry; Adila Formation, Pirgu Regional Stage; TUG 80-510 • 1 spec.; Vormsi Island, Saxby shore; Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-70 .</p><p>Description</p><p>The holotype (Fig. 24A) is a fragment of a phragmocone and a mature body chamber with parts of the outer shell preserved. The outer shell is apparently smooth at the position of the body chamber. The conch height at the base of the body chamber is 36 mm and the conch width 30 mm (CHI = 1.2). The conch cross section is oval, narrower at the ventral side. The phragmocone grows at a length of 33 mm from a conch height of 24 mm to 36 mm (angle of expansion = 21°) and the septa are 4.5 mm distant where the conch height is 35 mm (RCL = 0.13). The sutures are nearly directly transverse, forming only a very shallow lateral lobe. The septal foramen is 2 mm in diameter and positioned 2 mm from the conch margin where the conch height is 24 mm (RSH = 0.08, RSP = 0.09).</p><p>More complete mature body chambers are preserved in specimens GIT 878-70, TUG 80-510, TUG 1745-276 where a body chamber length of 32 mm is reached (0.9 of the corresponding conch height at the base of the body chamber). The conch height and width of the mature body chamber decreases toward the peristome with a convex outlines in lateral view. Probably a slight widening occurs at the adoral most part, resulting in an amphora-like apertural shape.</p><p>The conch dimensions vary very little among the four specimens: TUG 80-510 having the largest conch height with 37 mm and no smaller mature conch heights than 36 mm.</p><p>Comparison</p><p>This species is most similar to Danoceras fusiforme Balashov 1959, from the Rakvere Regional Stage of Estonia, which, however, has an even smaller mature size (maximum mature conch width = 19 mm). Diestoceras acuminatum Strand, 1934, which has a similar conch height at the base of the mature body chamber, can easily be distinguished from the new species in having an angle of expansion of the phragmocone of 28° (Strand 1934: 86).</p></div>	https://treatment.plazi.org/id/93268783964D701BFD9EFA24FD00FAC7	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783964B7066FE1BFAF2FB30FA13.text	93268783964B7066FE1BFAF2FB30FA13.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Danoceras piersalense (Teichert 1930) Kröger 2025	<div><p>Danoceras piersalense (Teichert, 1930) comb. nov.</p><p>Figs 16C–D, F, 24D, F–H, 25C, 26</p><p>Dowlingoceras (?) piersalense Teichert, 1930: 284, pl. 6 figs 17–18.</p><p>Dowlingoceras (?) piersalense – Strand 1934: 79. ― Miller &amp; Youngquist 1947: 415. ― Balashov 1953a: 208. ― Frye 1987: 95–96.</p><p>Emended diagnosis</p><p>Danoceras with compressed oval conch-cross section (CHI = 1.2–1.3); mature body chamber with maximum conch height near its base with height of ca 40–45 mm and height to length ratio of ca 0.8– 0.9; conch surface with distinct constriction near peristome and amphora-like apertural opening.</p><p>Material examined</p><p>ESTONIA • 1 spec.; Vormsi Island, Hosholm shore; Adila Formation, Pirgu Regional Stage; GIT 840-93 • 16 specs; Vormsi Island, Hosholm shore (tower locality); Adila Formation, Pirgu Regional Stage; GIT 426-988, GIT 840-261, GIT 840-270, GIT 840-258 a, GIT 840-272, GIT 878-263 to GIT 878-268, GIT 878-270 to GIT 878-272, GIT 878-276, GIT 878-279 • 1 spec.; same locality as for preceding; TUG 1745-48 • 2 specs; Pirgu River outcrops; Adila Formation, Pirgu Regional Stage; TUG 1745-296, TUG 1745-302 • 1 spec.; Vohilaid Island, Vohilaid shore (E); Adila Formation, Pirgu Regional Stage; GIT 878-267 .</p><p>Type locality and horizon</p><p>Piirsalu, Lääne County, in western Estonia; Moe Formation, Pirgu Regional Stage.</p><p>Description</p><p>None of the specimens assigned to this species is complete, all of them preserve parts of the mature or near mature body chamber and parts of the phragmocone. Specimen GIT 840-271 is a fragment of a mature specimen preserving the most important characters of this species. At the base of the body chamber, the conch height is 46 mm, the width cannot be is estimated as ca 36 mm. A length of 35 mm of the body chamber is preserved, where is has a convex outline and decreases to a conch height of 43 mm at its adoral end. The conch cross section is preserved near the adoral end of the phragmocone; it has a height of 42 mm and a width of ca 31 mm (CHI = 1.35) and an oval shape with a narrower margin at the ventral side. In a length of 39 mm, the phragmocone diameter increases from 31 mm to 41 mm (angle of expansion = 16°). The sutures form a shallow lateral sinus on the dorsal side. At a conch height of 40 mm, they are 6 mm apart (RCL = 0.1). On the surface of the internal mold of the phragmocone, faint longitudinal, ca 1 mm wide striae are visible. The siphuncular segments are subtrapezoidal (Fig. 16F). They have their greatest height near the adapical surface of the septa where they are broadly adnate. At a conch height of 37 mm, the septal distance is 4.2 mm, the greates height of the siphuncle 3.8 mm, and the septal foramen ca 2 mm. The septal necks are suborthochoanitic.</p><p>Amongst those specimens with complete mature body chamber preserved, their size, relative lengths, and cross section is slightly variable: in GIT 878-263 the conch height at the body chamber base is 44 mm, 38 mm at the peristome. The length of the body chamber is 44 mm (relative body chamber length = 1) and ca 10 mm from the peristome an inconspicuous constriction occurs (Fig. 25C). In TUG 1745-48, the conch height at the body chamber base is 44 mm, 37 mm at the peristome. The length of the body chamber is 30 mm (relative body chamber length = 0.68), and ca 10 mm from the peristome an inconspicuous constriction is present.</p><p>The mean relative body chamber length of all measured specimen is 0.79 (n= 18). The mean CHI at the base of the body chamber is 1.3 (n = 18) and the mean conch height at the base of the body chamber is 43 mm (n = 21, max. = 47 mm, min. = 40 mm). The frequency distribution of the mature conch sizes is bimodal: of the 21 specimens with mature body chamber preserved six specimens have a conch height of 40 mm at its body chamber base and four specimens have a conch height of 45 mm (Fig. 26A).</p><p>The conch cross section is oval, generally narrower on the ventral side, where it is almost angular in some specimens (e.g., TUG 1745-302, GIT 878-264; Fig. 24G). In specimen TUG 1745-302 the complete body chamber has a length of ca 35 mm, decreases in dorsoventral diameter from the base to the peristome and until ca 20 mm, where a shallow, inconspicuous constriction is present, beyond which, the body chamber diameter increases to ca 33 mm.</p><p>The sutures form wide, shallow lateral lobes, almost perpendicular to the growth axis, and a relatively deep saddle on the dorsum. The septa are spaced with a mean RCL of 0.12 (n = 56, max. = 0.13, min. = 0.09). In some specimens, narrow longitudinal furrows are visible on the surface of the internal mold of the phragmocone (e.g., TUG 1745-302, Fig. 24H). The conch surface is poorly preserved in all specimens and was apparently smooth on the mature body chamber and adjacent parts of the phragmocone.</p><p>The characters of the siphuncle are well-preserved in TUG 80-510 (Fig. 16C); at a conch height of 28 mm the septal foramen is circular with a diameter of ca 2.4 mm (RSH = 0.09). The septal necks are very short suborthochoanitic, and the connecting rings are expanded, forming subtrapezoidal segments with slightly convex outline in longitudinal view. The maximum diameter of the siphuncle is more than 3 mm. Near the adapical surface of the septum, the connecting ring is widest, forming a wide adnate area.</p><p>The siphuncle is also preserved in GIT 1745-296 at a position where the conch height is 34 mm and septa are 3.8 mm apart (RCL = 0.11). There, the septal foramen is 1.9 mm wide and 2.4 mm high (RSH = 0.07). The septal necks, which are poorly preserved, appear to be suborthochoanitic to cyrtochoanitic (Fig. 16D). The connecting ring forms subtrapezoidal siphuncular segments, which are widest and have a wide adnation area on the adapical surface of the septa (ca 3.8 mm).</p><p>Remarks</p><p>Teichert’s original diagnosis is emended here based upon the description and figures of Teichert (1930) and additional information from the specimens described here regarding the CHI, and the location and shape of the siphuncle. Most of the Estonian specimens are slightly deformed. The mean CHI therefore slightly overestimates the compression of the conch cross section. The type specimen, described by Teichert (1930) has a conch height at the base of the body chamber of 47 mm, and a conch width of 35 mm, and hence is larger than most of the specimens described herein, but falls within their range of variation. A bimodal frequency distribution of the mature conch size occurs in the material (Fig. 26A; supplementary data 4), but this does not allow for an unambiguous distinction of two species, because all morphological features measured form a continuum of variation.</p><p>Danoceras piersalense is identical in its mature size, rate of compression, and angle of phragmocone expansion to D. scandinavicum Strand, 1934 . The latter species has been distinguished from D. piersalense by its more convex adoral part of the phragmocone, which is also more sharply “marked out from the upper part of the conch” (Strand 1934: 84). These subtle differences are difficult to detect in the often fragmentary material from Estonia, and little is known about the variability of this character among species assigned to D. scandinavicum and D. piersalense . It is therefore highly likely, that D. scandinavicum represents a subjective junior synonym of D. piersalense or that both species are present in the Estonian material but remain undetected therein. Additional, and better-preserved material is needed to solve the problem. The species is assigned to Danoceras, herein, because of the Danoceras - like shape of siphuncle.</p><p>Comparison</p><p>This is a relatively large species of Danoceras, which can be distinguished from other late Katian species of the genus mainly by its size (conch height at the base of the mature body chamber 40–45 mm). The mature body chamber height of Danoceras breve Strand, 1934 (42 mm) is within the range of the specimens assigned to D. piersalense, herein, but differs in having a phragmocone with a higher angle of expansion (25°).</p><p>Dowlingoceras kallholnense Frye, 1987 and Danoceras scandinavicum Strand, 1934 have a mature body chamber of similar conch height at its base (40 mm, 39–42 mm, respectively) but their conch cross section is less compressed (CHI = 1.1–1.2), and the latter additionally is sharply curved on its ventral side. The mature body chamber height of Danoceras broeggeri Strand, 1934 is 56 mm.</p></div>	https://treatment.plazi.org/id/93268783964B7066FE1BFAF2FB30FA13	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396367067FDA8F9A6FEEBFBFC.text	9326878396367067FDA8F9A6FEEBFBFC.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Danoceras vohilaidense Kröger 2025	<div><p>Danoceras vohilaidense sp. nov.</p><p>urn:lsid:zoobank.org:act: 7564A1C1-841D-4E29-A39F-73A476806D3D</p><p>Fig. 24E</p><p>Diagnosis</p><p>Danoceras with compressed oval conch-cross section (CHI = 1.6) with narrow, almost angular, dorsal, and ventral margins; mature body chamber with maximum conch height near its base with height of ca 53 mm and height length ratio of ca 1.3; conch surface, with distinct constriction near peristome and amphora-like apertural opening.</p><p>Etymology</p><p>Refers to the type locality.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Vohilaid Island, Vohilaid shore (E); Adila Formation, Pirgu Regional Stage; GIT 878-273.</p><p>Paratypes</p><p>ESTONIA • 2 specs; same data as for holotype; GIT 878-274, GIT 878-278 .</p><p>Description</p><p>In all three specimens the outer shell is not preserved. In the holotype and in GIT 878-274, the conch height is 52–53 mm at the base of the body chamber, and at the peristome 48 mm, the conch width is 34 mm at the base of the body chamber (CHI = 1.56), and the length of the body chamber 40 mm. A slight taphonomic compression can be assumed, the conch cross section is oval with narrow, almost angular, dorsal, and ventral margins. In the holotype, the phragmocone has a height of 51– 47 mm at a length of 28 mm (angle of expansion = 8°). The sutures form very shallow lateral lobes, and the septal foramen is close to the conch margin with a width of 3.5 mm.</p><p>Remarks</p><p>The two mature body chambers (holotype and in specimen GIT 878-274) are almost identical in size and shape, identifying them as belonging to the same species. They are larger than those known from other Estonian Danoceras, and approximately similar to that of D. broeggeri Strand, 1934 from the Upper Isotelus Limestone of Norway. The latter differs in size and CHI (mature body chamber height 56 mm, CHI 1.3–1.4).</p></div>	https://treatment.plazi.org/id/9326878396367067FDA8F9A6FEEBFBFC	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396377067FD48FBF9FCB7F870.text	9326878396377067FD48FBF9FCB7F870.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Danoceras undefined-A	<div><p>Danoceras sp. A</p><p>Fig. 27D</p><p>Material examined</p><p>ESTONIA • Vormsi Island, Hosholm shore (tower locality); Adila Formation, Pirgu Regional Stage; GIT 878 -269.</p><p>Description</p><p>The specimen comprises parts of a nearly complete mature body chamber and four chambers of the phragmocone, lacking the outer shell. At the base of the body chamber, the conch height and width are 34 mm and 29 mm respectively (CHI = 1.12). The conch cross section is oval, compressed with narrow dorsal and ventral margins, the ventral (prosiphuncular) margin is narrower. The body chamber is 28 mm long, very slightly exogastrically curved. At its base, a narrow band of oncomyarian, buttressed muscle scars occur. A wide, inconspicuous constriction occurs ca 5 mm adapically from the peristome. The peristome is incompletely preserved, and the hyponomic sinus is not seen. At the peristome, the conch height is 32 mm. The sutures form shallow lateral lobes. The adoralmost two sutures are crowded. Adapically, the sutures are 5 mm apart, where the conch height is 33 mm. The siphuncle is preserved near the conch margin. The septal foramen is ca 2 mm wide and the siphuncular segments apparently are relatively narrow, Danoceras -like.</p><p>Remarks</p><p>This single specimen differs from all known species of Danoceras in its small mature size in combination with a relatively long and tubular body chamber. However, based on this single, fragmentary preserved specimen the erection of a new species is not possible.</p></div>	https://treatment.plazi.org/id/9326878396377067FD48FBF9FCB7F870	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396347064FDA7FEB1FDA7FD34.text	9326878396347064FDA7FEB1FDA7FD34.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Diestoceras Foerste 1924	<div><p>Genus Diestoceras Foerste, 1924</p><p>Type species</p><p>Gomphoceras indianense Miller &amp; Faber, 1894, Versailles, Indiana, USA, upper part of Hudson River group, Late Ordovician; by original designation.</p><p>Diagnosis</p><p>Short diestoceratids with straight or slightly curved shell, and circular conch cross section; conch reaches largest diameter at adoral end of mature phragmocone, contracting to aperture; peristome straight, transverse, with shallow hyponomic sinus; siphuncle positioned near conch margin, cyrtochoanitic; segments subquadrate in longitudinal section; thin annulosiphonate deposits with distinctive irregular linear processes, which extend adapically and adorally without fusing from segment to segment. (Compiled from Sweet 1964b.)</p></div>	https://treatment.plazi.org/id/9326878396347064FDA7FEB1FDA7FD34	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396347065FDDDFD40FC11FB61.text	9326878396347065FDDDFD40FC11FB61.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Diestoceras stensioei (Troedsson 1926)	<div><p>Diestoceras stensioei (Troedsson, 1926)</p><p>Fig. 27L, N</p><p>Cyrtogomphoceras stensioei Troedsson, 1926: 108–109, pl. 63 fig. 5, pl. 64 figs 1–2.</p><p>Diestoceras stoermeri Strand, 1934: 85 (partim).</p><p>Cyrtogomphoceras stensioei – Foerste 1929: 231.</p><p>Diestoceras stensioei – Teichert 1930: 294, 296. ― Miller &amp; Carrier 1942: 538. ― Flower 1946: 398. ― Balashov 1953a: 208. ― Stumbur 1956: 176. ― Flower in Flower &amp; Teichert 1957: 65. ― Zhuravlyeva 1962: pl. 26 fig. 6. ― Bolton 1977: 36.</p><p>Diagnosis</p><p>Diestoceras with slightly curved shell and compressed conch cross section; mature body chamber highest near its base with height of ca 80 mm, width of ca 65 mm and length of ca 30–50 mm; sutures straight, more narrowly spaced at venter. (Compiled from Troedsson 1926: 108–109.)</p><p>Material examined</p><p>ESTONIA • 5 specs; Vormsi Island, Hosholm shore (tower locality); Adila Formation, Pirgu Regional Stage; GIT 840-264, GIT 840-249 - 1, GIT 878-254, GIT 878-258, GIT 878-165 • 1 spec.; Piirsalu quarry; Moe Formation, Pirgu Regional Stage; GIT 426-987 • 4 specs; Vohilaid Island, Vohilaid shore (E); Adila Formation, Pirgu Regional Stage; GIT 878-253, GIT 878-255, GIT 878-259, GIT 878-262 .</p><p>Type locality and horizon</p><p>Rannaküla old quarry, near Haapsalu, western Estonia; Adila Formation, Pirgu Regional Stage.</p><p>Description</p><p>The most complete specimen is GIT 840-264 (Fig. 15N), which preserves parts of the mature body chamber and of the phragmocone. The complete cross section is not preserved but the conch height can be measured throughout the preserved parts of the conch. The maximum conch height of 74 mm is located at the base of the body chamber. Toward the peristome the conch height decreases to 58 mm at the peristome. The peristome is simple with a very shallow (ca 5 mm) hyponomic sinus. The outline of the mature body chamber in lateral view is convex. The cross section apparently circular or slightly compressed. At the base of the body chamber traces of a thin band of oncomyarian muscle scars are preserved; the band is ca 5 mm wide. The phragmocone has a convex outline in lateral view and decreases in diameter from 74 mm to 56 mm in 31 mm (angle of expansion = 32°). The septa are shallowly curved, 6 mm apart where the conch height is 68 mm (RCL = 0.09). No traces of the septal foramen or siphuncle are preserved.</p><p>The phragmocone is also well-preserved in GIT 878-259. It has a circular cross section and increases in diameter from 36 mm to 48 mm in a distance of 11 mm (angle of expansion = 43°). GIT 878-253, GIT 878-259, and GIT 878-262 preserve the circular conch cross section.</p><p>Remarks</p><p>This is a large Diestoceras . Other species known from Norway and Sweden reach mature diameters of ca 55 mm or less (Strand 1934; Frye 1987). Diestoceras breviconum (Portlock, 1843) reaches a smaller adult size (&lt;35 mm), and has a wider angle of expansion (38°).</p><p>In his description of Diestoceras stoermeri Strand, 1934, the author describes a specimen with a mature body chamber diameter of 75 mm as paratype (Strand 1934: 85). The holotype of this species has a conch diameter of only 50 mm at the base of the mature body chamber. The complete original diagnosis given for D. stoermeri is very brief and without explicitly mentioning the adult size: “Short rounded Diestoceras with circular cross section and low camerae” (Strand 1934: 85). Hence, based on the size of the holotype D. stoermeri has an adult diameter of ca 50 mm. Consequently, the paratype must be assigned to another, larger, species, which is most probably D. stensioei . Therefore, it can be assumed that this species occurs in the uppermost Katian strata (“Gastropod Limestone”) of Norway.</p><p>The holotype of C. stensioei differs slightly from the specimens described herein. The height of the mature body chamber of the holotype is 79 mm (compared with 74 mm in specimen GIT 840-264) and it has a compressed conch cross section (CHI = 1.22). However, Troedsson (1926) describes only the mature body chamber and not the conch cross section of the phragmocone and its intraspecific variability. Moreover, depending on the orientation of the specimens in the sediment and on the specific sediment stratum, various degrees of taphonomic compaction occur among the specimens. The deviations of the material described herein from the holotype are therefore interpreted as within the range of the intraspecific variability or as a result of taphonomic processes.</p></div>	https://treatment.plazi.org/id/9326878396347065FDDDFD40FC11FB61	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396357063FD43FB12FC37FC85.text	9326878396357063FD43FB12FC37FC85.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Diestoceras undefined-A	<div><p>Diestoceras sp. A</p><p>Fig. 27K</p><p>Material examined</p><p>ESTONIA • Vormsi Island, Hosholm shore (tower locality); Adila Formation, Pirgu Regional Stage; GIT 878 -252.</p><p>Description</p><p>The specimen preserves parts of the mature body chamber and the phragmocone. Two thirds of the shell (in longitudinal direction) are preserved, so that the conch cross section cannot be determined with certainty; but was apparently circular. The body chamber is 45 mm long. The conch height at the base of the body chamber is 64 mm, ca 10 mm adorally the conch height reaches its maximum at 67 mm and at the peristome the height is ca 57 mm. In longitudinal direction, the outline of the body chamber is convex, and the peristome is simple and directly transverse. The hyponomic sinus is not preserved. At the base of the body chamber, a ca 0.4 mm wide band of oncomyarian muscle scars is preserved. The phragmocone is slightly curved, its height increases from 30 mm to 62 mm at a length of 38 mm (angle of expansion = 46°). At a conch height of 62 mm, the sutures are 7 mm apart (RCL = 0.11). The sutures are straight and directly transverse. Traces of the septal foramen and siphuncle are not preserved.</p><p>Remarks</p><p>The short, rounded conch, simple mature peristome, and apparently circular conch cross section identify this specimen as a species of Diestoceras . The size of the mature body chamber differs from known species of the genus described from Baltoscandia. However, because of the fragmentary preservation of this single specimen a species level determination is not possible.</p></div>	https://treatment.plazi.org/id/9326878396357063FD43FB12FC37FC85	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396337063FDCBFC3FFAFCF9E6.text	9326878396337063FDCBFC3FFAFCF9E6.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Dowlingoceras Foerste 1928	<div><p>Genus Dowlingoceras Foerste, 1928d</p><p>Type species</p><p>Poterioceras gracile Whiteaves, 1892, Black Island, Swampy Harbour, Lake Winnipeg, Manitoba, Canada, Red River Formation, Katian; by original designation.</p><p>Diagnosis</p><p>Slender diestoceratids with straight or slightly curved shell, and elliptically compressed to oval conch cross section; mature body chamber with widest height and width near its base, with simple constriction close to mature aperture, with apertural widening and shallow hyponomic sinus; siphuncle positioned near conch margin, with, compared to other diestoceratids, narrow septal foramen and only slightly expanding segments. (Compiled from Teichert 1930, and Sweet 1964b.)</p><p>Comparison</p><p>Danoceras and Dowlingoceras differ mainly in the shape of the siphuncular segments (i.e., subtrapezoidal versus fusiform, respectively, Strand 1934: 80). In the Estonian material, a difference in the shape the mature body becomes also apparent: in Dowlingoceras, it is relatively long (ratio height / length ca one or more) and simple convex, while Danoceras has an adorally constricted, amphora-like body chamber.</p></div>	https://treatment.plazi.org/id/9326878396337063FDCBFC3FFAFCF9E6	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396337060FDDBF991FD57FB6B.text	9326878396337060FDDBF991FD57FB6B.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Dowlingoceras kallholnense Frye 1987	<div><p>Dowlingoceras kallholnense Frye, 1987</p><p>Figs 16E, 27A</p><p>Dowlingoceras kallholnense Frye, 1987: 95–96, figs 6a–b, 7.</p><p>Dowlingoceras kallholnense – Kröger 2013: tab.2.</p><p>Diagnosis</p><p>Dowlingoceras with a slightly compressed cross section (CHI = 1.1); oval cross section, venter narrower than dorsum; mature body chamber is more gibbous than those of the other species of the genus, ca 40 mm high at its base, and with marked constriction near the peristome. (Compiled from Frye 1987.)</p><p>Material examined</p><p>ESTONIA • Vormsi Island, Hosholm shore; Adila Formation, Pirgu Regional Stage; GIT 878-247.</p><p>Type locality and horizon</p><p>Kallholn, Dalarna, Sweden; Boda Formation, latest Katian.</p><p>Description</p><p>Specimen GIT 878-247 preserves parts of the mature body chamber and the phragmocone with a conch height and width of 39 mm and 32 mm, respectively (CHI = 1.2) The conch cross section is oval with a narrower curvature on the ventral compared to the dorsal side. The conch height increases from 36– 37 mm at a length of 17 mm (angle of expansion 8°). The body chamber is only partly preserved, had a length of more than 38 mm and decreases in conch height from its base with a convex outline in lateral view toward ca 35 mm in height. The sutures form a wide lateral lobe and are ca 6 mm apart where the conch height is 39 mm (RCL = 0.15). The siphuncular segments are elongated (7 mm long, 4 mm high, SCR = 0.57) fusiform, wider adorally and adnate to the adoral septal surfaces. The septal necks are poorly preserved, apparently cyrtochoanitic.</p><p>Remarks</p><p>The Swedish types of D. kallholnense have conch dimensions (maximum height of mature body chamber = 40 mm; CHI = 1.1, and a low angle of expansion in the adoral parts of the phragmocone) (Frye 1987) which are nearly identical to the specimen described herein. The differences in the connecting ring shape (presence of an adnate area in specimen GIT 878-247 are interpreted as taphonomic or the effects of orientation of the cut. (See also Turek &amp; Aubrechtová 2024, and Pohle et al. 2024, on this topic.) The view is oblique to the dorso-ventral body axis, in Frye (1987: fig. 7), it is apparently perpendicular to that axis in specimen GIT 878-247 (Fig. 16E).</p></div>	https://treatment.plazi.org/id/9326878396337060FDDBF991FD57FB6B	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396307061FDA7FB0DFB8CFC2E.text	9326878396307061FDA7FB0DFB8CFC2E.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Dowlingoceras tornense Kröger 2025	<div><p>Dowlingoceras tornense sp. nov.</p><p>urn:lsid:zoobank.org:act: 9E94767A-9B7E-440B-84D7-12F695042F30</p><p>Figs 25A–B, 27I</p><p>Diagnosis</p><p>Dowlingoceras with compressed elliptical conch-cross section (CHI = 1.3); mature body chamber with maximum conch height of ca 45 mm near its base and height to length ratio of ca 1, with a nearly straight, simple peristome and apparently lacking or only with a very shallow hyponomic sinus; angle of expansion of the phragmocone ca 12°.</p><p>Etymology</p><p>The Estonian “ torni ”, ‘towerʼ, refers to the type locality.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Vormsi Island, Hosholm shore (tower locality); Adila Formation, Pirgu Regional Stage; GIT 840-254.</p><p>Paratype</p><p>ESTONIA • same data as for holotype; GIT 840-273 .</p><p>Description</p><p>The holotype preserves parts the phragmocone and the mature body chamber. Where preserved (near the peristome), the conch surface is apparently smooth. The conch height and width at the base of the mature body chamber are 45 mm and 34 mm, respectively (CHI = 1.3). There, the shape of conch cross section is apparently elliptically to oval compressed. The ventral side is slightly more narrowly curved. In lateral view, the conch is straight. The body chamber is 46 mm long with a nearly straight, simple peristome and apparently without a hyponomic sinus. The lateral outline of the body chamber is slightly convex, reaching the greatest conch height 47 mm at ca mid-length location of the body chamber.</p><p>The phragmocone increases in height from 38 mm to 45 mm at a length of 32 mm (angle of expansion = 12°). The sutures form a shallow lobe at the lateral sides of the phragmocone, a sharp saddle on the ventral side and a rounded saddle on the dorsal side; they are 8 mm apart where the conch height is 42 mm (RCL = 0.19). The septal foramen is nearly marginal with a diameter of 5 mm where the conch height is 43 mm (RSH = 0.12). A natural cut of the siphuncle shows a fusiform, elongated, Dowlingoceras -like siphuncular segments (length 6 mm, height 3.8 mm, SCR = 0.63).</p><p>Comparison</p><p>The conch shape, including the shape of the mature body chamber is similar to that of D. kallholnense Frye, 1987 . However, the mature body chamber of D. tornense sp. nov. is greater in height, width, and length than that of D. kallholnense (40 mm, 36 mm, 40 mm, respectively, in D. kallholnense) and the conch cross section is more compressed (CHI = 1.1 in D. kallholnense).</p></div>	https://treatment.plazi.org/id/9326878396307061FDA7FB0DFB8CFC2E	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396317061FD6EFC48FDACF97D.text	9326878396317061FD6EFC48FDACF97D.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Dowlingoceras undefined-A	<div><p>Dowlingoceras sp. A</p><p>Fig. 27B–C, E</p><p>Material examined</p><p>ESTONIA • Vohilaid Island, Vohilaid shore (E); Adila Formation, Pirgu Regional Stage, GIT 878-249.</p><p>Description</p><p>The specimen is an internal mold of a mature body chamber with a conch height and width at its base of 44 mm and 38 mm, respectively (CHI = 1.2). At the peristome, the height and width are 40 mm and 32 mm, respectively. The body chamber is 36 mm long and in lateral view has slightly convex margins. The conch cross section is elliptical. At a distance of ca 10 mm from the peristome, a ca 10 mm wide and 1.5 mm deep constriction forms an amphora-like aperture. The peristome is directly transverse with a wide, inconspicuous hyponomic sinus on the prosiphuncular side. Traces of a septal foramen close to the conch margin are preserved.</p><p>Remarks</p><p>The specimen is assigned to Dowlingoceras based on shape of the mature body chamber. Its size and rounded elliptical cross section can be compared with D. torni, while the gibbous shape and terminal constriction can be compared with D. kallholnense . Based on this single incomplete specimen, erection of a new species is impossible.</p></div>	https://treatment.plazi.org/id/9326878396317061FD6EFC48FDACF97D	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
932687839631706EFD6DF905FBA8FCA5.text	932687839631706EFD6DF905FBA8FCA5.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Dowlingoceras undefined-B	<div><p>Dowlingoceras sp. B</p><p>Fig. 27J</p><p>Material examined</p><p>ESTONIA • Paope quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 47-866.</p><p>Description</p><p>The specimen is a straight, slightly deformed (compressed) fragment of ca eight chambers of the phragmocone and a nearly complete mature body chamber. At the base of the body chamber, the conch diameter is 47 mm, the diameter slightly increases adorally over a distance of ca 20 mm to 60 mm, then continuously decreases to a diameter of 58 mm near the aperture. A shallow and wide constriction is present ca 20 mm from the peristome. The peristome is only partially preserved. The body chamber is ca 60 mm long.</p><p>The phragmocone increases in diameter from 42 mm to 57 mm at a length of 52 mm (angle of expansion 16°). The sutures are straight and directly transverse while traces of the siphuncle are present near the conch margin, which are too poorly preserved measure. The remaining traces suggest that the siphuncle was fusiform.</p><p>Remarks</p><p>The poor preservation of this specimen does not allow further determination. The conch shape combined with the subfusiform siphuncle identify the specimen as a Dowlingoceras .</p></div>	https://treatment.plazi.org/id/932687839631706EFD6DF905FBA8FCA5	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783963E706EFDA5FCDEFC99F958.text	93268783963E706EFDA5FCDEFC99F958.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Diestoceratidae Foerste 1926	<div><p>Diestoceratidae gen. et sp. indet.</p><p>Fig. 27M</p><p>Material examined</p><p>ESTONIA • Salu; Pirgu Regional Stage; TUG 1745-192.</p><p>Description</p><p>The specimen is a fragment of a nearly straight mold of a mature body chamber and nine chambers of the phragmocone which is partially deformed. Parts of the shell are eroded. The conch surface is not preserved. The fragmentary preservation does not permit measurement of the original conch cross section. The maximum conch diameter (28 mm) is located at the base of the body chamber. The body chamber is ca 28 mm long with slightly convex conch margins, it contracts adorally to a diameter of ca 27 mm where a shallow, inconspicuous constriction is located ca 5 mm distant from the peristome. The phragmocone diameter increases from 23 mm to 27 mm at a length of 16 mm (angle of expansion = 18°). The sutures are directly transverse and 3.5 mm apart where the conch diameter is 27 mm (RCL = 0.13). On the surface of the phragmocone, faint longitudinal lirae may be seen.</p><p>Remarks</p><p>The conch shape, shape of the mature body chamber as well as spacing and pattern of sutures of this specimen are suggestive of a small diestoceratid. The small mature size and the relatively long body chamber are not known from any species of Danoceras, Dowlingoceras or Diestoceras described in the literature. However, as crucial features for determination, including the siphuncle position and shape, are not preserved, while the conch cross section cannot be fully be reconstructed, a genus and species level determination of this specimen is impossible.</p></div>	https://treatment.plazi.org/id/93268783963E706EFDA5FCDEFC99F958	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783963E706FFD99F89EFD8FFD5B.text	93268783963E706FFD99F89EFD8FFD5B.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Hiiumoceras Kröger 2025	<div><p>Genus Hiiumoceras gen. nov.</p><p>urn:lsid:zoobank.org:act: 18791ECD-C1D4-4806-9566-DC4C4B724F5A</p><p>Type species</p><p>Hiiumoceras hiiuense gen. et sp. nov. Hiiumaa Island, Estonia; Pirgu Regional Stage.</p><p>Diagnosis</p><p>Small, strongly curved, exogastric cyrtocones with short body chamber; circular conch cross section; siphuncle at some distance from conch margin (subventral); ornamented with fine, directly transverse striae.</p><p>Etymology</p><p>Refers to Hiiumaa Island, the region of the type species of this genus.</p><p>Comparison</p><p>The genus is very similar to Ringoceras Strand, 1934, from the Bønsnes Formation, late Katian, Ringerike, Norway, from which it differs in having a circular conch cross section and in lacking the longitudinal ornamentation.</p></div>	https://treatment.plazi.org/id/93268783963E706FFD99F89EFD8FFD5B	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783963F706DFDC9FD5DFB6CFE72.text	93268783963F706DFDC9FD5DFB6CFE72.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Hiiumoceras hiiuense Kröger 2025	<div><p>Hiiumoceras hiiuense gen. et sp. nov.</p><p>urn:lsid:zoobank.org:act: CBB9CFFF-F108-4D62-8667-64A3318EE96D</p><p>Figs 28A–D, 29A</p><p>Diagnosis</p><p>Same as for genus, by monotypy.</p><p>Etymology</p><p>Refers to the Hiiumaa, Estonia, the region, where this species is known from.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Hiiumaa Island, Paope quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 1745- 11.</p><p>Paratype</p><p>ESTONIA • 1 spec.; Hiiumaa Island, Paluküla quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-421 .</p><p>Description</p><p>The holotype is an exogastrically curved fragment of parts of a body chamber, and two chambers of the phragmocone. The conch cross section is circular with a diameter increasing from 16 mm to 22 mm and an angle of expansion of 16°. The outer shell is not preserved but on the surface of the inner mold, traces of directly transverse, shallow striae are visible. The sutures are 3 mm apart (RCL = 0.19), straight and directly transverse. A septal foramen with a diameter of 1 mm is preserved 2 mm from the conch margin, where the conch diameter is 16 mm (RSH = 0.06, RSP = 0.13). The septal necks are suborthochoanitic. The connecting rings are relatively thick and form nearly tubular segments; slightly expanded into the chambers (Fig. 29A). No endosiphuncular deposits are observed.</p><p>Specimen GIT 426-421 (Fig. 28A–D) is a mold of a complete body chamber with a circular conch-cross section increasing from 17 mm to 22 mm at a length of 20 mm (angle of expansion 18°). In lateral view, the dorsal margins and ventral margins of the body chamber are concavely and convexly curved, respectively. The conch expands gradually. On the surface of the specimen, shallow, directly transverse striae are visible (ca one per millimeter). The trace of a septal foramen is preserved at the base of the body chamber. It has a height of 2 mm and is 3 mm distant from the conch margin (RSH =0.11, RSP = 0.2).</p><p>Comparison</p><p>This species differs from the otherwise similar Ringoceras praecurvum Strand, 1934 in size, conch cross section and ornamentation. The Norwegian species is smaller (with an adult size of less than 20 mm), is additionally ornamented with longitudinal lirae, and has a compressed conch cross section.</p></div>	https://treatment.plazi.org/id/93268783963F706DFDC9FD5DFB6CFE72	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783963D706DFDB7FE07FBC2FCC6.text	93268783963D706DFDB7FE07FBC2FCC6.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Piersaloceras Teichert 1930	<div><p>Genus Piersaloceras Teichert, 1930</p><p>Type species</p><p>Piersaloceras gageli Teichert, 1930, from Piirsalu, Estonia; Moe Formation, Pirgu Regional Stage, late Katian; by original designation.</p><p>Diagnosis</p><p>Exogastric, gradually enlarging cyrtocones with nearly circular conch cross section and low angle of expansion; ornamented with low longitudinal ribs and distinct transverse frills; siphuncle nearly subcentrally positioned, cylindrical siphuncle. (Adopted from Teichert 1930.)</p></div>	https://treatment.plazi.org/id/93268783963D706DFDB7FE07FBC2FCC6	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783963A706AFDA1FC4CFDF1FA97.text	93268783963A706AFDA1FC4CFDF1FA97.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Kallholnoceras Frye 1987	<div><p>Genus Kallholnoceras Frye, 1987</p><p>Type species</p><p>Kallholnoceras cornutum Frye, 1987, Kallholn quarry, Kallholn, Dalarna, Sweden, Boda Formation, late Katian; by original designation.</p><p>Diagnosis</p><p>Exogastric, strongly curved cyrtocones with compressed conch cross section and gibbous mature body chamber; siphuncle close to conch margin, without endosiphuncular deposits with gradually enlarging; septal necks suborthochoanitic; siphuncle slightly expanded within chambers, without endosiphuncular deposits. (Compiled from Frye 1987.)</p></div>	https://treatment.plazi.org/id/93268783963A706AFDA1FC4CFDF1FA97	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783963B7069FDA2FD7CFAFDFEA3.text	93268783963B7069FDA2FD7CFAFDFEA3.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Beloitoceras Foerste 1924	<div><p>Genus Beloitoceras Foerste, 1924</p><p>Type species</p><p>Oncoceras pandion Hall, 1861, from Beloit, Wisconsin, USA, Black River Formation; by original designation.</p><p>Diagnosis</p><p>Strongly curved, relatively slender brevicones with ovate, compressed cross section; conch smooth or with fine transverse ornament; maximum conch diameter situated within adapical half to third of body chamber; antisiphuncular outline of conch concave over entire length in dorsoventral section, prosiphuncular outline broadly convex; five to eight chambers per distance similar to corresponding conch cross section; body chamber short with well-developed hyponomic sinus at convex side; siphuncle slender, situated close to convex margin of conch curvature, with subtubular segments; septal necks short suborthochoanitic to cyrtochoanitic; connecting rings thin. (Compiled from Sweet 1964b, and Frey 1995.)</p></div>	https://treatment.plazi.org/id/93268783963B7069FDA2FD7CFAFDFEA3	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396397069FDBCFED2FCF3FA8D.text	9326878396397069FDBCFED2FCF3FA8D.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Beloitoceras siljanense Frye 1987	<div><p>Beloitoceras siljanense Frye, 1987</p><p>Figs 29C, 30A</p><p>Beloitoceras siljanense Frye, 1987: 86–88, figs 3e–f, 4, 6c.</p><p>Beloitoceras siljanense – Kröger 2013: 20, figs 9c–d, 11, tab. 2. ― Pohle et al. 2022: fig. 2.</p><p>Diagnosis</p><p>Beloitoceras with compressed cross section; in longitudinal section, antisiphuncular conch margin nearly straight approaching mature peristome; angle of expansion of phragmocone typically more than 17°; mature conch with maximum height and width at peristome. (Adopted from Frye 1987.)</p><p>Material examined</p><p>ESTONIA • 1 spec.; Haapsalu holm; Adila Formation, Pirgu Regional Stage; TUG 939-56 .</p><p>Type locality and horizon</p><p>Kallholn, Dalarna, Sweden; Boda Limestone, late Katian.</p><p>Description</p><p>The specimen is a fragment of a phragmocone with a conch height that increases from 20 mm to 29 mm and respective conch width increasing from 13 mm to 21 mm (angle of expansion = 18°). The conch cross section is oval compressed with narrower prosiphuncular side (CHI: 1.4–1.5). The conch surface is not preserved. The sutures form shallow lateral lobes and rounded saddles on the venter and dorsum. Mid-laterally, the sutures are 3.3 mm apart where the conch height is 24 mm (RCL = 0.14). The septal necks are cyrtochoanitic. The siphuncle is relatively narrow, and slightly expanded within the chambers (Fig. 29C)</p><p>Remarks</p><p>This specimen can be identified as B. siljanense because of the characteristic straightened dorsal conch margin as well as of the relatively large angle of expansion.</p></div>	https://treatment.plazi.org/id/9326878396397069FDBCFED2FCF3FA8D	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396397077FDF6FA35FDCBFDD5.text	9326878396397077FDF6FA35FDCBFDD5.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Beloitoceras sinuososeptatum (Roemer 1861)	<div><p>Beloitoceras sinuososeptatum (Roemer, 1861)</p><p>Fig. 32A–B</p><p>Orthoceras sinuoso-septatum Roemer, 1861: pl. 6 fig. 3a–c.</p><p>Beloitoceras heterocurvatum Strand, 1934: 76, pl. 10 figs 8–9 (partim).</p><p>Richardsonoceras sinuososeptatum – Dzik 1984: 58, 188, text-fig. 16a–b, pl. 8 fig. 1a–d.</p><p>Beloitoceras heterocurvatum – Frye 1987: 84, fig. 3a–d. ― Kröger et al. 2011: 38, fig. 5a–b. Beloitoceras sinuososeptatum – Kröger 2013: 17–20, figs 9a–b, 11.</p><p>Diagnosis</p><p>Beloitoceras with compressed cross section and keeled conch margins on concave and convex side of conch curvature throughout entire length; in longitudinal section, antisiphuncular conch margin concave; angle of expansion of phragmocone ca 16–17°; length of body chamber somewhat less than maximum conch height; conch surface ornamented with irregularly spaced, rounded striae, which form a shallow sinus on the prosiphuncular side and a deep V-shaped sinus on the antisiphuncular side; about six chambers similar to the height of the conch cross section (RCL = 0.17); sutures with deep lateral lobes; siphuncle situated near ventral margin, segments ca twice as long as high (SCR = 0.5), with slightly convex vertical outline. (From Kröger 2013.)</p><p>Material examined</p><p>ESTONIA • 4 specs; Vormsi Island, Hosholm shore; Adila Formation, Pirgu Regional Stage; GIT 426- 110, GIT 840-248, GIT 840-92, GIT 840-251 • 3 specs; same data as for preceding; TUG 1743-76, TUG 1745-10, TUG 939-59 • 10 specs; Vormsi Island, Hosholm shore (tower locality); Adila Formation, Pirgu Regional Stage; GIT 426-2, GIT 840-256, GIT 840-267, GIT 840-268, GIT 878-237 to GIT 878- 239, GIT 878-241 to GIT 878-243 • 2 specs; Sutlepa quarry; Adila Formation, Pirgu Regional Stage; TAM G5:9, TAM G149:127 • 8 specs; Vardi manor ( Schwarzen); Adila Formation, Pirgu Regional Stage; TAM G5:1 to TAM G5:8 • 7 specs; Vohilaid Island, Vohilaid shore (E); Adila Formation, Pirgu Regional Stage; GIT 878-144 to GIT 878-146, GIT 878-151, GIT 878-152, GIT 878-240, GIT 878-244 • 1 spec.; same data as for preceding; TUG 1723-26 .</p><p>Type locality and horizon</p><p>Zawidowice by Oleśnica, Poland; erratic boulder, Vormsi–Pirgu regional stages (“Lyckholm Stufe” of Teichert 1930).</p><p>Remarks</p><p>The species has been revised and described in detail by Kröger (2013). The Estonian material adds to the knowledge of the variability of this species. Combined with the total dataset of 32 measurements, derived from the types from erratic boulders in Poland (Dzik 1984), the specimens known from Norway (Strand 1934), and Sweden (Kröger 2013), a decreasing angle of expansion is now evident for this species with ca 15°–20° in early growth stages and angles lower than 10° in nearly mature phragmocones (Fig. 33A). Conversely, the CHI increases during ontogeny (note, however, the possible taphonomic compression of some of the Estonian and Norwegian specimens; Fig. 33B). As with the Swedish material, the variability of the curvature of the conch varies quite strongly among specimens but distinct groups of weakly and strongly curved conchs could not be identified (compare, e.g., specimens TUG 939-59 and TUG 1723- 26, Fig. 32A–B). The largest known specimen has a height at the base of the mature body chamber of 44 mm (TUG 939-59, Fig. 32A).</p></div>	https://treatment.plazi.org/id/9326878396397077FDF6FA35FDCBFDD5	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396277074FDF0FDEDFBF3FE76.text	9326878396277074FDF0FDEDFBF3FE76.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Beloitoceras sinuoseptatum (Roemer 1861)	<div><p>Beloitoceras cf. sinuoseptatum (Roemer, 1861)</p><p>Figs 16G, 32C, 33</p><p>Material examined</p><p>ESTONIA • 2 specs; Vormsi Island, Hosholm shore; Adila Formation, Pirgu Regional Stage; GIT 878- 231, GIT 426-2.</p><p>Description</p><p>The nearly complete specimen GIT 878-231 (Fig. 32C) is relatively strongly curved during early growth stages (corresponding to conch heights &lt;ca 40 mm) and reaches a maximum conch height of 53 mm at the base of the mature body chamber. There, the conch width is ca 37 mm (CHI = 1.43), and the conch cross section is oval in shape with narrow dorsal and ventral margins. The body chamber is 35 mm long and at the aperture 48 mm high. In lateral view, the dorsal and ventral margin of the body chamber is slightly convex. The peristome appears to be straight and simple. The phragmocone height increases from 40 mm to 53 mm at a length of 55 mm (angle of expansion = 13°). Between conch heights of 21–40 mm the conch expands at an angle of 19°. The sutures form shallow lateral lobes.</p><p>In specimen GIT 426-2, which is a short fragment of a phragmocone with five chambers, the details of the siphuncle are well-preserved (Fig. 16G). The siphuncular segments are trapezoidal, with adnate areas at the adapical surfaces of the septa. The septal necks are cyrtochoanitic.</p><p>Remarks</p><p>The two specimens are slightly more curved and larger than the fragments assigned to B. sinuoseptatum but otherwise indistinguishable from the types and the material herein assigned to B. sinuoseptatum sensu stricto, in which a maximum conch height of ca 44 mm occurs (see above).</p></div>	https://treatment.plazi.org/id/9326878396277074FDF0FDEDFBF3FE76	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396247074FDBCFE00FABEF93D.text	9326878396247074FDBCFE00FABEF93D.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Beloitoceras uuemoisense Kröger 2025	<div><p>Beloitoceras uuemoisense sp. nov.</p><p>urn:lsid:zoobank.org:act: F793DBD7-51A6-4A8B-8939-F9372673A510</p><p>Fig. 28G–H</p><p>Diagnosis</p><p>Beloitoceras with a maximum conch height of ca 18 mm near mid-length of mature body chamber; compressed conch cross section with CHI of ca 1.35; angle of expansion of the phragmocone ca 20°, in lateral view ventral conch margin convex and dorsal conch margin concave throughout entire length; body chamber with constriction near mature peristome.</p><p>Etymology</p><p>Referring to the type locality.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Läänemaa, Uuemõisa; Adila Formation, Pirgu Regional Stage; TUG 1745-290.</p><p>Description</p><p>The holotype is a nearly complete conch of a small mature curved brevicone (Fig. 28G–H). Its greatest conch height of 17.5 mm occurs slightly adoral of the base of its body chamber, where the conch width is 13 mm (CHI = 1.35). At the base of the body chamber, the conch height is 17 mm and the corresponding width 12 mm (CHI = 1.42). The conch cross section is elliptical with nearly equally narrowly rounded dorsal and ventral margins. The body chamber is nearly straight, in lateral view its prosiphuncular margin is more curved (convex) than the antisiphuncular margin (concave). The conch height decreases toward the aperture with a marked constriction ca 2 mm from the peristome forming an amphora like apertural opening. The peristome appears to be straight transverse. The phragmocone is curved and increases in height from 11 mm to 17 mm at a length of 16 mm (angle of expansion = 21°). The sutures form wide lateral lobes, they are ca 2 mm apart where the conch height is 17 mm (RCL = 0.12). Details of the siphuncle are not known.</p><p>Comparison</p><p>This is a small species of Beloitoceras, superficially similar to species of Oncoceras . It differs from species of Oncoceras in having a gibbous mature body chamber and in lacking the convex portion of the conch margin at the antisiphuncular conch margin. The genus Beloitoceras is species rich, palaeogeographically widespread and stratigraphically relatively long ranging. Flower (1946) distinguished several groups within the genus. Beloitoceras uuemoisense sp. nov. can be placed in Flower’s (1946) group III of B. pandion Flower, 1946, which comprises faintly gibbous species with a concave conch margin at the antisiphuncular side. Within this group, B. uuemoisense is unique because of its small adult size of less than 20 mm.</p></div>	https://treatment.plazi.org/id/9326878396247074FDBCFE00FABEF93D	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396247075FD56F944FCA2FCD8.text	9326878396247075FD56F944FCA2FCD8.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Beloitoceras undetermined Foerste 1924	<div><p>Beloitoceras (?) sp.</p><p>Fig. 28F, I–J</p><p>Material examined</p><p>ESTONIA • 1 spec.; Raplamaa, Pirgu River outcrops; Adila Formation, Pirgu Regional Stage, GIT 426- 1081 .</p><p>Description</p><p>The specimen is a fragment of a nearly complete body chamber and part of a phragmocone. The conch is slightly exogastrically curved. The height and width of the 23 mm long phragmocone are 20–23 mm and 13.5–15 mm, respectively (angle of expansion = 8°; CHI = 1.4–1.5). The septa form wide lateral lobes and pointed angular saddles on the prosiphuncular side. The siphuncle is nearly marginal, empty and the septal foramen has a diameter of 1 mm at the apical end of the specimen (RSH = 0.05). The body chamber is slightly gibbous, reaching its greatest height of 24 mm at ca mid-length of the preserved part. Its preserved length is ca 25 mm.</p><p>Remarks</p><p>The relatively long and slender (but still gibbous) body chamber distinguishes this specimen from known species of Beloitoceras . Its uniqueness would justify the erection of a new species and genus. Alternatively, the specimen is related to Richardsonoceroides Kröger, Zhang &amp; Isakar, 2009, or Richardsonoceras priscum (Eichwald, 1860) (see below). However, knowledge about the shape of the complete mature body chamber and information on the siphuncle is needed for a definitive determination. The specimen therefore is left in open nomenclature.</p></div>	https://treatment.plazi.org/id/9326878396247075FD56F944FCA2FCD8	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396257075FDA0FCDCFD96FB03.text	9326878396257075FDA0FCDCFD96FB03.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Cyrtorizoceras Hyatt 1900	<div><p>Genus Cyrtorizoceras Hyatt, 1900</p><p>Type species</p><p>Cyrtoceras minneapolis Clarke, 1897, from Minneapolis, Minnesota, USA, Platteville Formation, Black River Group, Sandbian; by original designation.</p><p>Diagnosis</p><p>Compressed cyrtocones; dorsal and ventral profiles diverging constantly adorally; sides converging slightly over mature body chamber; aperture with deep hyponomic sinus; nearly smooth or ornamented with transverse costae; siphuncle subventral, slender; segments slightly expanded, probably empty. (Adopted from Sweet 1964b.)</p></div>	https://treatment.plazi.org/id/9326878396257075FDA0FCDCFD96FB03	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396257072FDA9FAB5FE2CFD42.text	9326878396257072FDA9FAB5FE2CFD42.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Cyrtorizoceras hariense Kröger 2025	<div><p>Cyrtorizoceras hariense sp. nov.</p><p>urn:lsid:zoobank.org:act: 08D1598D-B9FB-4C73-B47A-C2C7371DE0A7</p><p>Fig. 32E–F</p><p>Diagnosis</p><p>Large Cyrtorizoceras with nearly circular conch cross section, reaching a mature size of more than 60 mm; phragmocone expands at an angle of 18°–20°; conch only weakly curved; conch surface nearly smooth.</p><p>Etymology</p><p>Refers to Hari Strait, which is the sea strait west of Saxby shore, the type locality.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Vormsi Island, Saxby shore (N); Kõrgessaare Formation, Vormsi Regional Stage; GIT 878- 71.</p><p>Description</p><p>The holotype is a curved fragment of a phragmocone and a nearly complete body chamber. The conch surface is nearly smooth, ornamented with relatively coarse growth lines near the aperture. At the base of the body chamber, the conch cross section is circular or nearly so with a height of 48 mm. At the peristome, the width is 62 mm. The body chamber is 55 mm long, with a slightly curved growth axis, and in lateral view its dorsal and ventral margins have a concave and a convex curvature, respectively. The diameter of the body chamber increases continuously from its base toward the peristome. The phragmocone is 45 mm long and increases in diameter from 34 mm to 48 mm (angle of expansion = 18°). The sutures are directly transverse and 6 mm apart where the conch height is 45 mm (RCL = 0.13). The siphuncle is marginal or nearly so and expands into the chambers with a diameter of ca 5 mm where the chamber length is ca 6 mm (SCR = 0.83).</p><p>Remarks</p><p>This species of Cyrtorizoceras is unique in having large mature size in combination with a nearly circular conch cross section.</p></div>	https://treatment.plazi.org/id/9326878396257072FDA9FAB5FE2CFD42	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396227072FD51FD76FE5BF967.text	9326878396227072FD51FD76FE5BF967.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Cyrtorizoceras undefined-A	<div><p>Cyrtorizoceras sp. A</p><p>Fig. 32D</p><p>Material examined</p><p>ESTONIA • 1 spec.; Vohilaid Island, Vohilaid shore (E); Adila Formation, Pirgu Regional Stage; GIT 878-260 .</p><p>Description</p><p>The specimen is a fragment of an exogastrically curved mature body chamber and five chambers of the phragmocone. At the base of the body chamber, the conch height and width are 58 mm and ca 45 mm, respectively (CHI = 1.29), and the conch cross section is ovate, oval compressed with the prosiphuncular margin slightly narrower than the antisiphuncular margin. The preserved part of the body chamber is 22 mm in height. In lateral view, only the antisiphuncular side of the body chamber is sufficiently preserved to describe its shape; it is slightly concave throughout the preserved length. The prosiphuncular side is convex and more strongly curved than the antisiphuncular side. The phragmocone height expands with an angle of 26° through an increase in conch height of 48–58 mm. The sutures form a shallow lateral lobe and are slightly more adaperturally located on the antisiphuncular side of the conch. The adoral-most sutures are crowded and 4 mm distant. At a conch height of 53 mm the sutures are 5 mm apart (RCL = 0.09). The siphuncle is almost marginally positioned with segments that are expanded within the chambers.</p><p>Remarks</p><p>Like C. hariense sp. nov., C. sp. A is a large Cyrtorizoceras . It differs from C. hariense in being more compressed, in having a larger angle of expansion (angle of expansion = ca 20° in C. hariense) and a shorter mature body chamber. No similar species is known. Species of Diestoceras, which have similar high angles of expansion and short body chambers, may be distinguished by the contraction of the mature body chambers.</p></div>	https://treatment.plazi.org/id/9326878396227072FD51FD76FE5BF967	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396227073FDBEF911FACBFE83.text	9326878396227073FDBEF911FACBFE83.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Dalecarlioceras Frye 1987	<div><p>Genus Dalecarlioceras Frye, 1987</p><p>Type species</p><p>Dalecarlioceras bodense Frye, 1987, Kallholn, Dalarna, Sweden, Boda Limestone, latest Katian; by original designation</p><p>Diagnosis</p><p>Moderately to rapidly enlarging, cyrtoconic, exogastric brevicones with compressed conch cross section; mature body chamber gibbous with maximum gibbosity at mid-length, becoming compressed orad; dorsal conch profile straight to faintly concave, ventral conch profile moderately convex; aperture may be constricted with prominent hyponomic sinus; siphuncle situated close to venter, small in diameter, with tubular to fusiform segments, no endsiphuncular deposits known. (Adopted from Frye 1987.)</p></div>	https://treatment.plazi.org/id/9326878396227073FDBEF911FACBFE83	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396237073FDB3FE33FC94F8E2.text	9326878396237073FDB3FE33FC94F8E2.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Dalecarlioceras bodense Frye 1987	<div><p>Dalecarlioceras bodense Frye, 1987</p><p>Fig. 34D–F</p><p>Dalecarlioceras bodense Frye, 1987: 90–92, fig. 5a–b.</p><p>Diagnosis</p><p>Rapidly enlarging, large Dalecarlioceras with compressed conch cross section; mature body chamber gibbous with maximum width and height at mid-length of ca 65–70 mm, aperture compressed, unconstricted with well-defined hyponomic sinus; mature body chamber in lateral view with straight dorsal profile and convex ventral side throughout its length; siphuncle small and situated close to the venter. (Adopted from Frye 1987.)</p><p>Material examined</p><p>ESTONIA • 1 spec.; Paluküla quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-1099 • 1 spec.; Saaremõisa ( Lyckholm); Kõrgessaare Formation, Vormsi Regional Stage; TUG 1745-213 .</p><p>Type locality and horizon</p><p>Kallholn, Dalarna, Sweden; Boda Limestone, latest Katian.</p><p>Description</p><p>The better-preserved of the two specimens is TUG 1745-213 (Fig. 34A–B); it is a mold of a complete mature body chamber and one chamber of the phragmocone. The specimen is slightly deformed. At the base of the body chamber, the conch height and width are 58 mm and 57 mm, respectively (CHI = 1.02). The cross section is nearly circular, with a slightly narrower margin on the prosiphuncular side. The length of the body chamber is 56 mm. In lateral view, the body chamber is nearly straight with convex margins on the pro- and antisiphuncular sides. Deformation during diagenesis has caused the antisiphuncular margin to be more curved than the prosiphuncular side. The greatest height is reached at ca mid-length of the body chamber with 66 mm. The peristome is slightly constricted with a height of 65 mm. The peristome is too poorly preserved to recognize the hyponomic sinus if present. At the base of the body chamber, traces of a thin, ca 5 mm wide, oncomyarian band of muscle-scars is preserved. The preserved chamber of the phragmocone is 5 mm long. The sutures are straight and directly transverse. The septal foramen is ca 1 mm distant from the conch margin and 6 mm in diameter (RSH = 0.09, RSP = 0.02).</p><p>The second specimen is a poorly preserved portion of a body chamber and one chamber of the phragmocone with a conch height of 60 mm at the base of the body chamber and a maximum height of 63 mm at the mid-length of the body chamber. The preserved length of the body chamber is 47 mm. The conch cross section of the specimen was apparently sub-circular.</p><p>Remarks</p><p>The two specimens described above can be assigned to D. bodense based on the similarities of the conch shape and dimensions with the types of this species.</p></div>	https://treatment.plazi.org/id/9326878396237073FDB3FE33FC94F8E2	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396237071FDDCF894FEE6FADC.text	9326878396237071FDDCF894FEE6FADC.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Dalecarlioceras constrictum Frye 1987	<div><p>Dalecarlioceras constrictum Frye, 1987</p><p>Figs 29D, 34A–B</p><p>Dalecarlioceras constrictum Frye, 1987: 92–93, fig. 3g –h.</p><p>Dalecarlioceras constrictum – Kröger 2013: 24, fig. 7a, tab.2.</p><p>Diagnosis</p><p>Moderately expanding Dalecarlioceras with curved, relatively short conch and compressed conch cross section; mature body chamber gibbous with maximum conch height of ca 44 mm, not greatly inflated; mature aperture constricted apicad of peristome, aperture height is one-fourth of body chamber length; peristome with well-developed hyponomic sinus. (Adopted from Frye 1987.)</p><p>Material examined</p><p>ESTONIA • 2 specs; Vormsi Island, Hosholm shore (tower); Adila Formation, Pirgu Regional Stage; GIT 878-248, GIT 878-251.</p><p>Type locality and horizon</p><p>Kallholn, Dalarna, Sweden; Boda Limestone, latest Katian.</p><p>Description</p><p>Specimen GIT 878-248 is a fragment of a mature body chamber and three chambers of the phragmocone. The conch surface is poorly preserved. Near the peristome, it is almost smooth with fine, irregularly spaced growth lines. At the base of the body chamber, the conch height and widths are 41 mm and 35 mm, respectively (CHI = 1.1). The body chamber is gibbous, 35 mm long, and in lateral view has convex outlines with the greatest conch height of 44 mm 20 mm adoral of the base of the body chamber. The phragmocone increases in height from 40 mm to 34 mm at a length of 18 mm (angle of expansion = 19°). The sutures form shallow lateral lobes and are 6 mm apart where the conch height is 38 mm (RCL = 0.16). The siphuncle is nearly marginal, has fusiform segments and is without endosiphuncular deposits. The septal necks are suborthochoanitic to cyrtochoanitic (Fig. 29D).</p><p>In GIT 878-251, a nearly complete mature body chamber and seven chambers of the phragmocone are preserved (Fig. 34A–B). At its base the body chamber is 37 mm high, and 34 mm wide (CHI = 1.1), has a broad elliptical conch cross section, and a gibbous form in lateral view. The greatest height is reached ca 20 mm adorad from its base (ca 44 mm), its total length is 43 mm. The mature peristome has a ca 7 mm deep, wide hyponomic sinus developed on the prosiphuncular side. The height of the phragmocone increases from 27 mm to 37 mm at a length of 31 mm (angle of expansion 18°). The siphuncle is located near the conch margin, its segments are fusiform (siphuncular height = 3.2 mm, segment length = 5.5 mm).</p><p>Remarks</p><p>The species was described in detail by Frye (1987). The Estonian specimens are very similar to the Swedish types.</p></div>	https://treatment.plazi.org/id/9326878396237071FDDCF894FEE6FADC	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783962E707EFDC0FE24FD2DFCA0.text	93268783962E707EFDC0FE24FD2DFCA0.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Richardsonoceras Foerste 1933	<div><p>Genus Richardsonoceras Foerste, 1933</p><p>Type species</p><p>Cyrtoceras simplex Billings, 1857, from Nepean township, Ottawa, Ontario, Canada, Leray Formation, Sandbian; by original designation.</p><p>Diagnosis</p><p>Gradually enlarging strongly curved shells; cross section compressed with elliptical to oval cross section, convex side of conch curvature more narrowly rounded; adult body chamber slightly contracted adorally; sutures with shallow lateral lobe, slightly oblique sloping slightly adapically on the antisiphuncular side; siphuncle small, close to margin on convex side of conch curvature; segments slightly expanded. (Adopted from Kröger et al. 2009b: 286.)</p></div>	https://treatment.plazi.org/id/93268783962E707EFDC0FE24FD2DFCA0	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783962E707DFE3AFCD4FBCFFC98.text	93268783962E707DFE3AFCD4FBCFFC98.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Richardsonoceras priscum (Eichwald 1860) Kröger 2025	<div><p>Richardsonoceras priscum (Eichwald, 1860) comb. nov.</p><p>Fig. 35C–D</p><p>Cyrtoceras priscum Eichwald, 1860: 1285, pl. 47 fig. 10a–c.</p><p>Beloitoceras (?) estonicum Teichert, 1930: 292, pl. 6 figs 11–12.</p><p>Richardsonoceras nikiforovae Balashov, 1962b: 114–115, 128, pl. 46 fig. 5a–b.</p><p>Richardsonoceras nikiforovae – Zhuravlyeva 1962: pl. 23 fig. 4.</p><p>“ Richardsonoceras ” nikiforovae – Dzik 1984: 63, 67, text-fig. 18.34.</p><p>Oonoceras priscum – Dzik &amp; Kiselev 1995: 66, fig. 2 (non fig. 1f–g, fig. 3c–d).</p><p>Emended diagnosis</p><p>Richardsonoceras with a relatively weak conch curvature, with an angle of expansion of ca 8°; oval compressed conch cross section with CHI of 1.2–1.6 which increases with conch height; mature conch height ca 18 mm.</p><p>Material examined</p><p>ESTONIA • 13 specs; Hiiumaa Island, Kõrgessaare quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-129, GIT 878-130, GIT 426-387, GIT 426-388, GIT 426-390, GIT 426-397 to GIT 426- 399, GIT 426-428, GIT 426-554, GIT 426-607 to GIT 426-609.</p><p>Type locality and horizon</p><p>Kõrgessaare quarry, Hiiumaa island, Estonia; Kõrgessaare Formation, Vormsi Regional Stage (Lyckholm Stage of Teichert 1930).</p><p>Description</p><p>The most complete specimen (GIT 426-608, Fig. 35C) is a deformed (compressed), curved fragment of a mature body chamber, and possessing at least ten chambers of the phragmocone. The phragmocone increases in height from 11.5 mm to 18 mm (angle of expansion of 8°). The conch height at the base of the body chamber is 14 mm and its preserved length ca 35 mm. The peristome is not preserved. In lateral view, the dorsal and ventral conch margins are concave and convex, respectively, throughout the entire length of the body chamber. The adoralmost part of the body chamber appears to be less curved than the rest of the specimen. The sutures form wide lateral lobes and distinct and sharp saddles on the prosiphuncular side. They are 2 mm apart where the conch height is 12 mm (RCL = 0.17). The two adoralmost septa are crowded. Traces of a narrow siphuncle (0.7 mm in width) are preserved near the conch margin. The siphuncular segments expand slightly into the chambers.</p><p>The oval compressed conch cross section is well-preserved in specimen GIT 426-399, with a CHI of 1.3 at a conch height of 13 mm. There, the conch margin on the prosiphuncular side is narrower rounded than on the antisiphuncular side.</p><p>The CHI increases during ontogeny from ca 1.2 at a conch height of 10 mm (specimen GIT 878-129) to 1.5 at conch a height of 18 mm (specimen GIT 426-608). The mean angle of expansion is 10° (range: 6°–15°, n = 5). The high variability results from deformation during the diagenesis of the specimens. The mean RCL is 0.13 (range: 0.1–0.15, n = 6).</p><p>Remarks</p><p>The material described herein provides for the first time a comprehensive overview of this species, which has a complicated history. The original description of Cyrtoceras priscum Eichwald, 1860 is based on a specimen from near Kõrgessaare, Hiiumaa Island (Eichwald 1860: 1285). An original from the Eichwald collection was figured in Dzik &amp; Kiselev (1995: fig. 2) and designated as the lectotype of “ Oonoceras priscum (Eichwald, 1861) ” (sic). Earlier, Teichert (1930) had designated a small fragment, also from Kõrgessaare, Hiiumaa Island, as type of his new species Beloitoceras (?) estonicum Teichert, 1930 noting its similarity to C. priscum (Teichert 1930: 271) . However, based on the single, fragmentary type of B. (?) estonicum and the single fragment available from the Eichwald collection in St Petersburg, he could only speculate regarding a possible synonymy of the two species. The additional material described above comes exclusively from the Kõrgessaare Formation, Vormsi Stage of Kõrgessaare, the type locality of C. priscum and B. (?) estonicum . The new material shows that B. (?) estonicum must be considered a junior synonym of C. priscum, and that this species is best placed within Richardsonoceras . The placement with Richardsonoceras is preferred over Beloitoceras because of the slender, non-gibbous or only very weakly gibbous mature body chamber of this species.</p><p>It is now clear that this species is identical in size and shape to R. nikiforovae Balashov, 1962b; described from the Dolborian Regional Stage, Katian, of the Siberian platform and which should be considered as a subjective junior synonym of C. priscum .</p><p>The complication arises from a misinterpretation of the stratigraphical horizon from which Eichwald’s type originated by Dzik &amp; Kiselev (1995: 66). They literally translated Eichwald’s “calcaire à Orthocératites” as the “ Orthoceras limestone” of later authors, which is late Darriwilian in age. However, Eichwald (1860) generally termed Ordovician limestone strata as “calcaire à Orthocératites”, as is evident from his descriptions of other specimens collected from Late Ordovician strata. There is no evidence that the Kõrgessaare specimens are from glacial boulders of Darrwilian age, and the specimens described above are clearly from a Kõrgessaare Formation lithology.</p><p>This stratigraphic misinterpretation probably led Dzik &amp; Kiselev (1995) to synonymize a specimen figured in Dzik (1984: text-fig. 15a, pl. 9 fig. 1), which significantly differs from C. priscum in having a lower angle of expansion, a wider chamber spacing and a nearly circular conch cross section and thus represents a different species. Hence, C. priscum is a genuine late Katian Richardsonoceras, presently known only from Kõrgessaare, Hiiumaa Island.</p><p>Comparison</p><p>Several specimens are deformed and / or are only fragmentarily preserved, making a definite determination of the conch curvature difficult. However, three comparatively well-preserved specimens (GIT 426-607, -608, GIT 878-129) reveal the relatively low degree of curvature of the conch compared with other species of Richardsonoceras . The species of Richardsonoceras described from the Black River Group (Foerste 1932, 1933) have a stronger conch curvature. All, except R. simplex (Billings, 1857), also have a larger mature conch height (&gt; 20 mm). The mature size of R. bellatulum Sweet &amp; Miller, 1957 from the Cape Phillips Formation, Cornwallis islands, Canada, is similar than that of R. estonicum, but the Cape Phillips species is also more strongly curved (see also Balashov 1962b: 115).</p></div>	https://treatment.plazi.org/id/93268783962E707DFE3AFCD4FBCFFC98	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783962D707DFD97FC19FAB6FB13.text	93268783962D707DFD97FC19FAB6FB13.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Rizosceras Hyatt 1884	<div><p>Genus Rizosceras Hyatt, 1884</p><p>Type species</p><p>Orthoceras indocile Barrande, 1866 from Kocorc, Bohemia, Czech Republic, Middle Silurian; by original designation.</p><p>Diagnosis</p><p>Compressed, rapidly enlarging, straight to faintly curved brevicones with hyponomic sinus and distinct, faintly rugose transverse surficial ornament; siphuncle ventrally positioned near conch margin; septal necks cyrtochoanitic; siphuncular segments cardioid in dorsoventral section. (Adopted from Sweet 1964b.)</p></div>	https://treatment.plazi.org/id/93268783962D707DFD97FC19FAB6FB13	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783962D707AFD78FAA3FDAFF9D3.text	93268783962D707AFD78FAA3FDAFF9D3.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Rizosceras teres Kröger 2025	<div><p>Rizosceras teres sp. nov.</p><p>urn:lsid:zoobank.org:act: 8A906D01-DEF8-402F-9CF3-7CCE72E51F9B</p><p>Figs 27F, 28E, 29B</p><p>Diagnosis</p><p>Rizosceras with nearly smooth conch surface, ornamented only with fine, irregularly spaced growth lines or lirae; mature conch height ca 45 mm; phragmocone expands with an angle of ca 20°; conch cross section slightly elliptically compressed; siphuncle close to conch margin, with expanded segments, which are wider at their adoral ends.</p><p>Etymology</p><p>Refers to the Latin ‘ teres ’ (‘fine’, ‘well-rounded’) because of its relatively smooth conch surface.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Saaremõisa (Lyckholm); Kõrgessaare Formation, Vormsi Regional Stage; TUG 1745-188.</p><p>Paratypes</p><p>ESTONIA • 2 specs; Kõrgessaare quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426- 550, GIT 426-1141 • 1 spec.; Vormsi Island, Saxby shore; Kõrgessaare Formation, Vormsi Regional Stage; TUG 80-508 .</p><p>Description</p><p>The holotype, TUG 1745-188 (Figs 27F, 28E), is a slightly deformed (compressed) fragment of a phragmocone and a body chamber. The conch surface was apparently smooth. The conch height increases at a length of 25 mm from of 22 mm to 30 mm (angle of expansion = 18°). The sutures are straight and directly transverse, 5 mm apart where the conch height is 25 mm (RCL = 0.2). The siphuncle is close to the conch margin at a conch height of ca 22 mm. There, the septal foramen is almost marginally positioned and has a width of 2 mm. The siphuncular segments are fusiform, expanded into the chambers, wider near the adoral septal surface.</p><p>Specimen GIT 426-550 (Fig. 30B) is a fragment of a body chamber and one chamber of the phragmocone, it has a length of 28 mm and an apical angle of 20°. The conch surface is nearly smooth, ornamented with fine, irregularly spaced growth lines or lirae. At its apical end, the conch height and width are 32 mm and 27 mm, respectively (CHI = 1.18). Its maximum conch height is ca 43 mm at the peristome. The peristome is simple, directly transverse; no traces of a hyponomic sinus are visible at the venter, which is relatively poorly preserved. In lateral view, the body chamber is nearly conical, straight, with a very slight convexity at the dorsal and ventral sides. The relatively narrow spacing of the two preserved septa indicates that this is a body chamber of a mature specimen. The sutures are 4 mm apart where the conch height is 32 mm (RCL = 0.13) and are straight and directly transverse. The septal foramen is located near the conch margin but too poorly preserved to be measured.</p><p>In specimen TUG 80-508, the septal foramen is ca 3 mm in diameter and the siphuncle expands toward 6 mm into the chambers where the septa are 7 mm apart and the conch height is ca 30 mm (RSH = 0.1, SCR = 0.9).</p><p>Remarks</p><p>This new species is placed in Rizosceras based on similarity of the general conch shape, the shape of the siphuncular segments, and the position of the siphuncle in the type-species of this genus. Its relatively smooth surface could be used as an argument to erect a new genus, similar to Rizosceras, but with a smooth conch surface. Rizosceras is a very species rich and long ranging genus (see e.g., Barskov 1972) probably containing unrelated species with similar conch shapes and ornamentation. A revision, therefore, would be desirable but is out of scope of this work. Moreover, the erection of a new genus, based on relatively poorly preserved fragments of Rizosceras teres sp. nov. seems unwise until better material is available and a detailed comparison with the type species of the genus is possible.</p><p>Comparison</p><p>This is a Rizosceras with a relatively smooth surface, low angle of expansion and a relatively strongly curved apical conch part. The shape of the mature body chamber almost resembles the Silurian Metarizoceras Foerste, 1930b .</p></div>	https://treatment.plazi.org/id/93268783962D707AFD78FAA3FDAFF9D3	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783962A707BFDB4F926FB53FC83.text	93268783962A707BFDB4F926FB53FC83.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Deckeroceras Foerste 1935	<div><p>Genus Deckeroceras Foerste, 1935a</p><p>Type species</p><p>Deckeroceras adaense Foerste, 1935a, from Ada, Pontotoc County, Oklahoma, USA, lower Fernvale Formation, late Katian; by original designation.</p><p>Diagnosis</p><p>Strongly exogastrically curved conch with nearly circular cross section, becoming depressed at the aperture of the mature body chamber; broad and shallow hyponomic sinus; siphuncle positioned near venter but not marginal; siphuncular segments nearly tubular, slightly contracted near septal foramens. (Adopted from Foerste 1935a: 93.)</p><p>Remarks</p><p>The sutures of this genus have been described as having a ventral sutural lobe in a previous genus diagnosis (Flower 1943a: 262; Sweet 1964a: K382). This is erroneous. In the original diagnosis, a ventral sutural lobe is not mentioned (Foerste 1935a: 92) and in the description of the type of the genus, the sutures are described as follows: “The sutures of the septa curve only slightly downward laterally, both the dorsal and ventral margins reaching about the same level transversely” (Foerste 1935a: 93). “Downward” here probably refers as directed toward the apex, and thus, Foerste (1935a) described a shallow lateral lobe instead of a ventral lobe in Deckeroceras . The phrase “curve downward” in (Foerste 1935a: 93) could also refer to the distal ends of the lateral suture. This issue can only be definitely resolved by revisiting the type material, which is beyond the scope of this work. Deckeroceras has been placed within the Apsidoceratidae by Flower (1943a) and Sweet (1964a: K382) without explicit justification. A classification of this genus is equally possible within the Uranoceratidae (based on the family diagnosis given in Sweet 1964a: K374). Here, Deckeroceras is provisionally placed within the Uranoceratidae, to emphasize the similarity of this genus with Warburgoceras Kröger, 2013 and its relation to the early evolution of the Ascocerida (see discussion in Kröger 2013: 83, 100).</p></div>	https://treatment.plazi.org/id/93268783962A707BFDB4F926FB53FC83	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783962B7079FDAEFC33FE41FEA1.text	93268783962B7079FDAEFC33FE41FEA1.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Deckeroceras balticum Kröger 2025	<div><p>Deckeroceras balticum sp. nov.</p><p>urn:lsid:zoobank.org:act: 05BFB795-1743-407B-8866-5030650628D2</p><p>Fig. 36A</p><p>Winnipegoceras sp. – Teichert 1930: 294, pl. 8 fig. 23.</p><p>Diagnosis</p><p>Deckeroceras with mature conch height of ca 65 mm, nearly circular to slightly compressed conch cross section at mature body chamber; mature body chamber strongly curved and contracted.</p><p>Etymology</p><p>Refers to type region.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Vohilaid Island, Vohilaid shore (E): Adila Formation, Pirgu Regional Stage; GIT 878-227.</p><p>Description</p><p>The specimen is a fragment of a mature body chamber and five chambers of the phragmocone. The outer shell of the specimen is not preserved. At the base of the body chamber, the conch is ca 65 mm high. At the apical end of the specimen, 32 mm from the base of the body chamber, the conch height is 49 mm, and the conch cross section was nearly circular or slightly compressed. The angle of expansion of the phragmocone is ca 28°. The sutures are directly transverse and 8 mm apart where the conch height is 49 mm (RCL = 0.15). The siphuncle and the septal foramen are either not preserved or not visible. The body chamber is strongly curved and ca 65 mm long. In lateral view the convex side of the conch is much more strongly curved than the concave side, resulting in a relatively narrow mature aperture (height ca 40 mm).</p><p>Remarks</p><p>A specimen from Piirsalu, Estonia, figured and described in Teichert (1930), is identical in size and shape, and can be assigned to the same species, based on the knowledge of this more complete specimen, described herein.</p><p>Comparison</p><p>The two other species of this genus ( D. adaense, D. clermontense Foerste 1935b, known from the type-region and from the Elgin Member of the Maquoketa Shale, Iowa, USA) have smaller adult sizes (maximum conch heights 40–50 mm), and in D. clermontense Foerste, 1935a the mature body chamber is less strongly curved.</p></div>	https://treatment.plazi.org/id/93268783962B7079FDAEFC33FE41FEA1	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396297079FDCFFE69FC22FCF4.text	9326878396297079FDCFFE69FC22FCF4.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Schuchertoceras Miller 1932	<div><p>Genus Schuchertoceras Miller, 1932</p><p>Type species</p><p>Ascoceras anticostiensis Billings, 1866, Junction cliff, Anticosti Island, Canada, probably from Ellis Bay Formation, Hirnantian, Late Ordovician; by original designation.</p><p>Diagnosis</p><p>Ascoceratid cephalopods with basal non-ascoceroid septum between septum of truncation and the first ascoceroid septum in mature conch. (Adopted from Frye 1982.)</p></div>	https://treatment.plazi.org/id/9326878396297079FDCFFE69FC22FCF4	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396297046FE3EFC80FBF4FA62.text	9326878396297046FE3EFC80FBF4FA62.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Schuchertoceras deformis (Eichwald 1860) Kröger 2025	<div><p>Schuchertoceras deformis (Eichwald, 1860) comb. nov.</p><p>Fig. 36D, F–G</p><p>Ascoceras deforme Eichwald, 1860: 1192, pl. 42 fig. 18.</p><p>Billingsites deformis – Foerste 1929: 157, pl. 20 fig. 3. ― Strand 1934: 54–55, pl. 4 fig. 7. ― Frye 1982: 1278.</p><p>non Billingsites deformis – Sweet &amp; Miller 1957: 43, pl. 4 figs 1–2.</p><p>Diagnosis</p><p>Schuchertoceras with three ascoceroid septa which are detached from each other throughout their entire length; with elliptically depressed conch cross section and nearly straight growth axis in ascoceroid growth stages.</p><p>Material examined</p><p>ESTONIA • 1 spec.; Haapsalu holm; Adila Formation, Pirgu Regional Stage; TUG 46-138 • 1 spec.; Läänemaa, Uuemõisa; Adila Formation, Pirgu Regional Stage; TUG 2-734 • 1 spec.; Vohilaid Island, Vohilaid shore (E); Adila Formation, Pirgu Regional Stage; GIT 878-191 .</p><p>Type locality and horizon</p><p>Kõrgessaare quarry, Hiiumaa Island; Kõrgessaare Formation, Vormsi Regional Stage.</p><p>Description</p><p>TUG 2-734 is the most complete specimen (Fig. 37F–G), which preserves an almost complete ascoceroid portion of the conch including the basal septum, three ascoceroid septa and the nearly complete mature peristome. The width of the specimen is 36 mm at the basal septum, 47 mm at approximate, mid-length where it reaches its maximum width, and 35 mm at the aperture. The conch cross section is elliptically depressed (CHI: 0.75–0.85), but not completely preserved in portions between ca 20 mm from the aperture and 10 mm from the apical end. At the aperture, the height is 28 mm; at the basal septum the height can be reconstructed as ca 27 mm and its maximum height can be reconstructed as ca 40 mm. In lateral view, the conch is nearly straight and egg-shaped with a rounded but narrow apical tip and a constricted adoral part with a simple straight peristome. The ventral (prosiphuncular) margin of the peristome is poorly preserved, and the presence of a shallow shallow hyponomic sinus cannot be excluded. The maximum height is reached at ca 25 mm from the aperture. The basal suture is directly transverse at ca 17 mm from the apical end of the specimen. On the dorsum, the respective distances of the ascoceroid sutures from the peristome are 8 mm, 14 mm, and 23 mm. In lateral view, they form a pointed lateral lobe at ca 10 mm from the basal septum and a wide lateral sinus.</p><p>The ventral part and the interior of the basal septum are well-preserved in TUG 46-138. The ventral part is shallowly convex in lateral view and in cross section. The basal septum is located at a conch width of 38 mm and the septal foramen is in a nearly marginal position (ca 2 mm from ventral margin) with a diameter of ca 4 mm (RSH = 0.1, RSP = 0.06).</p><p>The third specimen (GIT 878-191) is a poorly preserved, deformed fragment of an ascoceroid conch with the three ascoceroid sutures and a straight peristome preserved (Fig. 36D).</p><p>Remarks</p><p>These specimens can be referred to Ascoceras deforme Eichwald, 1860 based on the three ascoceroid septa, which are clearly visible in Eichwaldʼs (1860: pl. 49 fig. 18) figures. There, the basal septum is not figured or is not preserved, which is the reason why this species was classified within Billingsites Hyatt, 1884 in Foerste (1929) and Strand (1934). Strand’s (1934) identification of the genus was questioned by Frye (1982: 1278) but the poorly preserved material to hand at the time did not permit a solution to the problem. The faint suture of the basal septum can easily be overlooked. In the material described above it is best visible in specimen TUG 46-138.</p><p>Comparison</p><p>Schuchertoceras deformis differs from the two species of Schuchertoceras known from the Boda Limestone of Dalarna, Sweden in having three instead of two (in S. bodense Frye, 1982) or one (in S. troedssoni (Foerste, 1929)) ascoceroid septa, and in its more slender conch. It differs from North American species of Schuchertoceras in having ascoceroid sutures which are detached from each other throughout their entire length (compare Frye 1982: fig. 3a–j).</p><p>The specimen described under Billingsites deformis (Eichwald, 1860) ? by Sweet &amp; Miller (1957) does not belong to this species because it has less than three ascoceroid septa and probably no basal septum. Additionally, the shape of the ascoceroid septum, visible in Sweet &amp; Miller (1957: pl. 4 figs 1–2) differs considerably from that of the Estonian specimens in that it is less strongly curved.</p></div>	https://treatment.plazi.org/id/9326878396297046FE3EFC80FBF4FA62	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396167046FDB6FA48FD12F87F.text	9326878396167046FDB6FA48FD12F87F.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Redpathoceras Flower 1963	<div><p>Genus Redpathoceras Flower, 1963</p><p>Type species</p><p>Redpathoceras clarki Flower, 1963, northeast of Joliette, Quebec, Canada; Leray Limestone, early to middle Katian, Ordovician; by original designation.</p><p>Diagnosis</p><p>Gyrocones with circular to depressed mature conch cross section; mature body chamber inflated with greatest diameter at approximate mid-length; broad shallow hyponomic sinus; septum of truncation deeply rounded; sutures of septa in mature specimen slightly oblique, sloping in adoral direction on concave side of conch curvature; siphuncle eccentric, close to conch margin at convex side of conch curvature. (Adopted from Flower 1963.)</p></div>	https://treatment.plazi.org/id/9326878396167046FDB6FA48FD12F87F	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396177045FDBFFEB0FD20FB9F.text	9326878396177045FDBFFEB0FD20FB9F.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Redpathoceras saxbyense Kröger 2025	<div><p>Redpathoceras saxbyense sp. nov.</p><p>urn:lsid:zoobank.org:act: CABFDC93-1BC6-4CF4-A4EA-EF32E10648D4</p><p>Figs 36B–C, E, 37E</p><p>Diagnosis</p><p>Redpathoceras with weakly annulated mature body chamber, which is ornamented with irregularly spaced, transverse lirae or frills; exogastrically curved mature body chamber with nearly circular conch cross section at base and depressed at aperture, ca 45 mm high and 70 mm long.</p><p>Etymology</p><p>Refers to the type locality.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Vormsi Island, Saxby shore (N); Kõrgessaare FormationVormsi Regional Stage; GIT 426- 346.</p><p>Paratypes</p><p>ESTONIA • 2 specs; same data as for holotype; GIT 878-84, GIT 878-156 • 1 spec.; Moe stratotype outcrop; Moe Formation, Pirgu Regional Stage; TUG 76-97 • 1 spec.; Salu; Pirgu Regional Stage; TUG 1745-316 • 1 spec.; Vohilaid Island, Vohilaid shore (E); Adila Formation, Pirgu Regional Stage; GIT 878-236 .</p><p>Description</p><p>GIT 426-346 (Fig. 36B–C) is a fragment of a mature body chamber and two chambers of the phragmocone. The outer shell is poorly preserved and apparently smooth or with fine irregular rounded lirae. The conch cross section at the base of the body chamber is nearly circular (conch height = 45 mm, conch width = 43 mm). The body chamber is 68 mm long and exogastrically curved. In lateral view, the antisiphuncular margin of the body chamber has a convex, and the prosiphuncular side a concave outline with an increasingly narrow conch cross section toward the aperture. The outline undulates slightly, resulting from a weak irregular annulation. Approximately two annulations occur on the body chamber. They are oblique, slightly shifted orad at the antisiphuncular side. At the aperture, the conch cross section is depressed with a height of 35 mm and a width of ca 25 mm, respectively. The sutures are directly transverse and 6 mm apart where the conch height is 45 mm (RCL = 0.13). There, the septal foramen has a diameter of 4.5 mm and is 5 mm distant from the conch margin.</p><p>GIT 878-156 is a weakly exogastrically curved fragment of a phragmocone and part of a body chamber showing the details of the siphuncle and septal necks (Fig. 37E). The phragmocone height increases from 34 mm to 41 mm at a length of 27 mm (angle of expansion = 15°). The conch cross section is slightly compressed (CHI = 1.07). The septa form directly transverse sutures, 7 mm apart where the conch height is 37 mm (RCL = 0.19). The septal foramen is ca 4.5 mm in diameter and ca 5 mm distant from the conch margin (RSH = 0.12, RSP = 0.16). The siphuncular segments are nearly tubular and the septal necks are loxochoanitic dorsally and suborthochoanitic ventrally.</p><p>In TUG 76-97 (Fig. 36E), and TUG 1745-316 the conch surface of the mature body chamber is well-preserved. In the three specimens, the shell is slightly irregularly annulated, similar to GIT 426-346. Additionally, the conch surface is ornamented with irregularly spaced rounded lirae (ca one to two per millimeter) which are slightly shifted orad on the dorsum.</p><p>Comparison</p><p>This species of Redpathoceras differs from other species of the genus in having a weakly annulated and transversally frilled mature body chamber. A specimen, assigned by Evans (1993) to Charactoceras ? cinerum (Blake, 1882), probably represents another similarly ornamented species of Redpathoceras, which has, however, a larger adult size (mature body chamber 60 mm wide and 200 mm long).</p><p>The possibility exists that the specimens described herein are related to Piersaloceras gageli Teichert, 1930, which is known only from a single immature fragment, or to another, yet to be discovered species of Piersaloceras . This is suggested based on the similar ornamentation and similar position of the siphuncle. If this is the case, Piersaloceras could be interpreted as an uranoceratid or probillingsitid. The strongly curved, isolated, body chamber described herein under Piersaloceras (?) sp. (Fig. 30C), would support such a hypothesis. Because of the fragmentary character of the known specimens, however, this relation must remain speculative, for now.</p></div>	https://treatment.plazi.org/id/9326878396177045FDBFFEB0FD20FB9F	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396157045FDDBF9AFFC47F83C.text	9326878396157045FDDBF9AFFC47F83C.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Cyrtogomphoceras Foerste 1924	<div><p>Genus Cyrtogomphoceras Foerste, 1924</p><p>Type species</p><p>Oncoceras magnum Whiteaves, 1890, East Selkirk, Selkirk Member, Red River Formation, late Katian, Ordovician, by original designation</p><p>Diagnosis</p><p>Compressed endogastric cyrtocones with fusiform outline in lateral view; rapidly expanding in adoral part of mature phragmocone and/ or basal part of mature body chamber; mature body chamber gibbous, conically contracted; aperture with hyponomic sinus; sutures with shallow lateral lobes, sloping increasingly toward the antisiphuncular side of the conch in later growth stages; siphuncle large, not strictly marginal, with short cyrtoconic septal necks, thick connecting rings, and endosiphuncular bullettes, cameral deposits absent. (Adopted from Teichert 1964b.)</p></div>	https://treatment.plazi.org/id/9326878396157045FDDBF9AFFC47F83C	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396157045FDFAFB58FBCCFA15.text	9326878396157045FDFAFB58FBCCFA15.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Cyrtogomphoceratidae Flower 1940	<div><p>Family Cyrtogomphoceratidae Flower, 1940</p><p>Remarks</p><p>The genera (especially the new genera) placed within the Cyrtogomphoceratida vary widely in features, such as chamber spacing, siphuncular shape, and in conch shape. Here, following Teichert (1964b) I placed all endogastrically curved brevicones with expanded siphuncular segments into this family. A family revision and probably the erection of a new family for Hosholmoceras gen. nov. are required, but a revision of the Cyrtogomphoceratidae is beyond the scope of this work.</p></div>	https://treatment.plazi.org/id/9326878396157045FDFAFB58FBCCFA15	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396127043FDFEFEB0FDE3FAC9.text	9326878396127043FDFEFEB0FDE3FAC9.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Cyrtogomphoceras troedssoni Teichert 1930	<div><p>Cyrtogomphoceras troedssoni Teichert, 1930</p><p>Figs 37B, 38C–D</p><p>Cyrtogomphoceras (?) troedssoni Teichert, 1930: 296–297, pl. 8 figs 32–33.</p><p>Faberoceras troedssoni – Flower 1946: 452.</p><p>Cyrtogomphoceras (?) troedssoni – Balashov 1953a: 208.</p><p>Faberoceras? troedssoni – Flower in Flower &amp; Teichert 1957: 66, 91, text-fig. 27.</p><p>Diagnosis</p><p>Small Cyrtogomphoceras with conch height of mature body chamber ca 40 mm, slightly compressed conch cross section (CHI ca 1.1) and irregularly, transversally constricted and undulating conch surface; sutures straight, directly transverse; siphuncle marginally located with very widely expanded segments; septal necks cyrtochoanitic, recumbent; small to moderate endosiphuncular bulletes.</p><p>Material examined</p><p>ESTONIA • 1 spec.; Hiiumaa Island, Kõrgessaare quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-392-1 • 1 spec.; same data as for preceding; TUG 939-60 .</p><p>Description</p><p>GIT 426-392-1 (Fig. 38D) is a fragment of an endogastrically curved phragmocone and mature body chamber, with the outer shell partly preserved. The conch surface is hidden under an overgrowth of epibionts, but a fine transverse striation is visible on the inner mold of parts of the body chamber. At the base of the mature body chamber, the conch height and width are 40 mm and 35 mm, respectively (CHI = 1.14). The conch cross section has an oval shape with a narrower prosiphuncular side. The body chamber is at least 43 mm long and slightly curved with a convex antisiphuncular margin and a concave prosiphuncular margin. At its adoral end, the height of the body chamber is 38 mm. The peristome is either not preserved, or only very fragmentarily preserved. In lateral view, the entire specimen (body chamber and phragmocone) appears slightly irregularly undulated with shallow constrictions at irregular distances. The phragmocone has a height of 30–40 mm at a length of 36 mm (angle of expansion = 15°). The sutures are straight and directly transverse and 7 mm apart where the conch height is 35 mm (RCL = 0.2). The siphuncle is marginal and very wide, it is too poorly preserved to measure the septal foramen. The segments have a height of 9 mm where the chamber length is 6 mm, and the conch height is 32 mm (SCR = 1.5).</p><p>The second specimen TUG 939-60 is a short fragment of the phragmocone and body chamber, showing the typical irregular undulation of the shell (Fig. 38C). At a conch height of 40 mm, the conch width its 35 mm, similar to GIT 426-392-1. The sutures are straight and directly transverse. The siphuncle and septal necks are well-preserved in this specimen (Fig. 37B). The siphuncle is very wide; the septal foramen has a height of 9 mm and the siphuncular segments expand toward 15 mm where the chamber length is 5 mm, the conch height is 40 mm (RSH = 0.23, RSS = 1.67, SCR = 3). The connecting ring is thin, the septal necks are cyrtochoanitic recumbent and small endosiphuncular bullettes are present.</p><p>Remarks</p><p>This species is unique to Cyrtogomphoceras with regard to its relatively small size (the type species C. magnum Whiteaves, 1890 has a conch length of ca 270 mm) and its slightly irregularly undulated shell. C. cf. thompsoni Miller &amp; Furnish, 1937, from the late Katian of Norway (Sweet 1959) is more curved, slightly larger (ca 70 mm maximum conch height) and the adoral-most sutures are more oblique than in C. troedssoni Teichert, 1930 .</p></div>	https://treatment.plazi.org/id/9326878396127043FDFEFEB0FDE3FAC9	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396137040FDA9FAECFB93FE1B.text	9326878396137040FDA9FAECFB93FE1B.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Hosholmoceras Kröger 2025	<div><p>Genus Hosholmoceras gen. nov.</p><p>urn:lsid:zoobank.org:act: 67E22CEA-BE72-42D4-9847-5F0A216039FC</p><p>Type species</p><p>Hosholmoceras ovalis gen. et sp. nov. from Hosholm shore, Vormsi Island, Estonia, Adila Formation, Pirgu Regional Stage.</p><p>Diagnosis</p><p>Endogastrically curved brevicones with very short chambers (RCL ca 0.05–0.07); conch cross section compressed or subtriangular; in lateral view mature conch slightly gibbous with largest conch heights near the base of the mature phragmocone; mature body chamber short, simple conical; sutures with shallow lateral lobes; siphuncle marginal, small; siphuncular segments rounded, expanded; septal necks cyrtochoanitic; endosiphuncular bulettes occur.</p><p>Etymology</p><p>Hosholm is the type locality of this genus.</p><p>Comparison</p><p>This genus is superficially similar to Hemibeloitoceras Balashov, 1962b, in having very short chambers (RCL ca 0.08) and a relatively thin, marginal siphuncle with simple expanded siphuncular segments. However, the conch of Hemibeloitoceras is exogastrically curved, expands gradually and is slenderer (angle of expansion ca 8°) while the sutures are directly transverse without a lateral lobe. Another curved breviconic form with very short chambers is Antiphragmoceras Foerste, 1925 . This also differs from Hosholmoceras gen. nov. in having an exogastrically curved conch.</p></div>	https://treatment.plazi.org/id/9326878396137040FDA9FAECFB93FE1B	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
932687839610704EFDC9FD9CFC76FE1F.text	932687839610704EFDC9FD9CFC76FE1F.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Hosholmoceras ovalis Kröger 2025	<div><p>Hosholmoceras ovalis gen. et sp. nov.</p><p>urn:lsid:zoobank.org:act: 221233FB-02D1-4F7C-A010-B574D890913D</p><p>Figs 37C, 39E–G</p><p>Diagnosis</p><p>Elliptically to oval compressed Hosholmoceras gen. nov., with CHI of ca 1.3–1.5, with angle of expansion of up to ca 26°, maximum mature conch size of ca 50 mm, mature body chamber length of ca 30 mm; ornamented with fine, narrowly spaced transverse lirae.</p><p>Etymology</p><p>The name refers to Hosholm, Vormsi Island, the type locality.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Vormsi Island, Hosholm shore ( tower locality); Adila Formation, Pirgu Regional Stage; GIT 840-252.</p><p>Paratypes</p><p>ESTONIA • 3 specs; same data as for holotype; GIT 878-171 to GIT 878-173 • 11 specs; Vohilaid Island, Vohilaid shore (E); Adila Formation, Pirgu Regional Stage; GIT 878-170, GIT 878-174 to GIT 878-177, GIT 878-179 to GIT 878-184 .</p><p>Description</p><p>The holotype is an endogastrically curved, compressed fragment of a phragmocone and body chamber (Fig. 39G). The conch is slightly deformed (compressed). Parts of the outer shell are preserved on the antisiphuncular margin near the adoral end of the specimen. There, it is ornamented with fine transverse lirae of which ca 8 occur per 5 mm where the conch height is 53 mm. In lateral view, the pro-, and antisiphuncular conch margins, respectively, are convex and concave throughout their entire length. The concave side is nearly straight adorally, so that in lateral view the entire specimen has a bulbous shape. The greatest width is near the adoral end of the phragmocone. The greatest rate of expansion occurs in adapical parts of the phragmocone, where it increases in height from 28 mm to 42 mm over a distance of ca 30 mm (angle of expansion = 26°). The length of the preserved part of the body chamber is 20 mm. The conch cross section is rounded elliptical to oval with a slightly narrower margin at the antisphuncular side. At the base of the body chamber the height and width are 52 mm and 34 mm, respectively (CHI = 1.53). At the apical end of the specimen, the height and width are 28 mm and 21 mm, respectively (CHI = 1.33). The sutures are narrowly spaced, ca 2–3 mm apart throughout the entire length of the phragmocone (RCL ca 0.05–0.07). The sutures form wide lateral lobes. Details of the siphuncle and septal necks are preserved at the apical end of the specimen (Fig. 37C). The septal foramen is nearly marginal (ca 1 mm from the conch margin), very small (ca 1 mm in diameter, RSH = 0.04) and the septal necks are cyrtochoanitic. The siphuncular segments are rounded, expanded within the chambers with a width of 4 mm where the chamber length is ca 1.8 mm (SCR = 2.2). Thin bullettes are present.</p><p>Three other specimens in the collection (GIT 878-170, GIT 878-181, GIT 878-183) have a maximum conch height of ca 50–52 mm, suggesting that this is the mature size of this species. A nearly complete body chamber is preserved in specimen GIT 878-170 (Fig. 39E–F), it is simple conical, 23 mm long, and has a straight peristome at the antisiphuncular side of the conch.</p><p>Remarks</p><p>See Remarks on Hosholmoceras triangulatum gen. et sp. nov. (below).</p></div>	https://treatment.plazi.org/id/932687839610704EFDC9FD9CFC76FE1F	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783961E704EFDFCFD98FBF6F83E.text	93268783961E704EFDFCFD98FBF6F83E.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Hosholmoceras triangulatum Kröger 2025	<div><p>Hosholmoceras triangulatum gen. et sp. nov.</p><p>urn:lsid:zoobank.org:act: CF3EC75F-3CF1-464E-A7B4-2AFC3874F932</p><p>Fig. 39A–B, D</p><p>Diagnosis</p><p>Slender Hosholmoceras gen. nov. (angle of expansion ca 15°), with rounded triangular conch cross section, with CHI ca 1, maximum mature conch size of ca 50 mm, and mature body chamber length of ca 30 mm; ornamented with fine, narrowly spaced transverse lirae.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Vormsi Island, Hosholm shore; Adila Formation, Pirgu Regional Stage; TUG 119-2.</p><p>Paratypes</p><p>ESTONIA • 2 specs; same data as for holotype; GIT 878-168, GIT 878-169 • 1 spec.; Vohilaid Island, Vohilaid shore (E); Adila Formation, Pirgu Regional Stage; GIT 878-178 .</p><p>Description</p><p>The holotype is a fragment of the phragmocone and the mature body chamber. The conch surface is not preserved (Fig. 39A–B, D). The conch is endogastrically curved (siphuncle at the concave side of the conch curvature). The complete conch cross section is preserved only in the apical portion of the specimen. There, it is rounded triangular with three sides of equal width and a narrowly rounded venter. The siphuncle is not visible or not preserved but apparently lies in the mid-position on the flat dorsum. At the apical end, the conch height and width are ca 27 mm and 26 mm, respectively. The greatest width of the specimen is reached ca 80 mm in the adoral direction from apical end of the specimen with 45 mm (angle of expansion = 14°). Beyond this point, the conch width decreases and at the base of the body chamber is ca 42 mm. The greatest conch width is located ca 20 mm adorally from the base of the body chamber. The preserved part of the body chamber is ca 25 mm long. The sutures forms shallow lateral lobes; they are narrowly spaced, ca 15–20 occur in a distance equal to the corresponding conch height (RCL ca 0.05–0.07).</p><p>Specimen GIT 878-169 is a small fragment of a phragmocone with ca four chambers preserved, it shows the rounded triangular conch cross section where the conch height and width are 32 mm and 37 mm, respectively (CHI = 0.86). The third specimen is a poorly preserved fragment of a phragmocone with a triangular conch cross section with a conch width of 27 mm.</p><p>Remarks</p><p>The siphuncle is only poorly preserved in the four specimens available. The poor preservation of the siphuncle is also a feature that can be seen in H. ovalis sp. nov. Amongst the 14 specimens of H. ovalis available for study only two preserved traces of the thin marginal siphuncle. Hosholmoceras triangulatum sp. nov. is similar to the type species of Hosholmoceras in having extremely narrowly spaced chambers and a bulbous phragmocone but differs in having a triangular conch cross section.</p></div>	https://treatment.plazi.org/id/93268783961E704EFDFCFD98FBF6F83E	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783961F704FFDA9FEB1FDCCF859.text	93268783961F704FFDA9FEB1FDCCF859.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Kiaeroceras Strand 1934	<div><p>Genus Kiaeroceras Strand, 1934</p><p>Type species</p><p>Kiaeroceras frognoyense Strand, 1934, from Frognoyøa island, Ringerike, Norway, “ Trinucleus limestone, (4cβ)” (Strand 1934: 98), SØrbakken Formation, Late Katian; by original designation.</p><p>Diagnosis</p><p>Orthocones with ovate conch cross section, narrower ventral conch margin; mature body chamber slightly bulbous, with shallow constriction near aperture; aperture with deep and broad hyponomic sinus; sutures with lateral lobes and pronounced ventral saddle; siphuncle close to ventral conch margin, with broadly expanded siphuncular segments, with prominent bullettes. (Adopted from Strand 1934.)</p><p>Remarks</p><p>The diagnosis of the genus given in Kröger (2013) is imprecise, it is corrected herein and features now the important characters described in Strand (1934). Moreover, the relatively rich Estonian material described herein reveals a few features, not known from type material of the type species. These include the shape and dimensions of the more apical phragmocone parts, variability in conch cross section shape as well as the extent and development of endosiphuncular deposits. Consequently, species are included here, which have conch cross sections with a CHI of nearly 1, although possessing the characteristically narrow margin on the prosiphuncular side. Additionally, the hyponomic sinus which is deep in the type species, does not seem to be deep in all species. Finally, the more complete specimens of this genus reveal that the curvature is endogastric and that the suture develops a lateral lobe during the latest growth stages (compare, e.g., Fig. 34H, and Strand 1934: pl. 9 fig. 4 and pl. 12 fig. 2). The genus is interpreted here sensu lato, to include these deviations from the original diagnosis.</p><p>The genus was placed within the Cyrtogomphoceratidae by Teichert (1964b) and has been compared to Protophragmoceras by Strand (1934). This was based on the presence of heavy endosiphuncular bullettes in the type-material. The new material, described herein, shows that in specimens assigned to Kiaeroceras transitions exist from typical discosorid-like bullettes toward valcouroceratid-like actinosiphonate deposits (see below in description of K. kaebliki sp. nov.).</p><p>Moreover, Strand (1934) described Mixosiphonoceras norvegicum Strand, 1934 from late Katian strata in Norway. The type species of Mixosiphonoceras is mid Silurian in age and the genus is placed within the Brevicoceratidae, which are known otherwise only from the mid Silurian to Devonian. Therefore, it is likely that the Norwegian species represents another Kiaeroceras .</p><p>The presence of actinosiphonate deposits in endogastrically curved Kiaeroceras, in orthocones ( Mixosiphonoceras norvegicum Strand, 1934), and in exogastrically curved valcouroceratids suggests either multiple independent origins of this type of endosiphuncular deposit or a close relationship between these taxa. A detailed phylogenetic, or cladistic analysis of the oncocerid-discoserid groups, which could help to solve this open question (suggested also by Pohle et al. 2022) is beyond the scope of this work.</p><p>Below, four species of Kiaeroceras are described in open nomenclature. These are known almost exclusively from their mature body chambers. Their differing sizes and shapes are unique, and they differ from species described in the literature and herein. However, the relatively low number of known specimens of Kiaeroceras does not permit evaluation of the intraspecific and interspecific variability in, e.g., mature body chamber size, and CHI. The possibility therefore exists, that some of these species, represent intraspecific variability.</p></div>	https://treatment.plazi.org/id/93268783961F704FFDA9FEB1FDCCF859	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783961C704DFD9DFEB1FC4AFBBC.text	93268783961C704DFD9DFEB1FC4AFBBC.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Kiaeroceras kaebliki Kröger 2025	<div><p>Kiaeroceras kaebliki sp. nov.</p><p>urn:lsid:zoobank.org:act: 50E19EA5-FCD5-4F44-8B9A-2A14C1789E05</p><p>Figs 37F, H, 40C, G</p><p>Diagnosis</p><p>Kiaeroceras with a CHI of 1.2, with an adult body chamber height of less than 40 mm; mature body chamber slightly longer than high (RBL ca 1.1).</p><p>Etymology</p><p>From the small bird Käblik (Estonian), referring to the small size of this species.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Vormsi Island, Saxby shore; Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-31.</p><p>Paratypes</p><p>ESTONIA • 2 specs; same data as for holotype; GIT 426-1123, GIT 878-158 • 1 spec.; Sutlema quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-163</p><p>Description</p><p>Specimen GIT 878-31 is an orthoconic fragment of a mature body chamber and parts of the phragmocone. At the base of the body chamber, the conch height is 37 mm and the width 32 mm (CHI = 1.2). The outer shell is not preserved but the conch surface was apparently smooth. The conch cross section is oval, the conch margin on the prosiphuncular side is more narrowly curved. The body chamber is 40 mm long and has a simple, straight peristome with an inconspicuous, wide hyponomic sinus, ca 3 mm deep, at the antisiphuncular side. The conch height is 34 mm at the peristome. In lateral view, the body chamber is slightly convex, its greatest width occurs at the adapical third of the length with a conch height of 38 mm. The phragmocone height increases from 35 mm to 37 mm at a length of 17 mm (angle of expansion = 7°). The sutures form wide, shallow lobes laterally and have a distance of 5 mm where the conch height is 37 mm (RCL = 0.14). The siphuncle (Fig. 37H) is nearly marginal with a septal foramen 4 mm in diameter, where the conch height is 37 mm (RSH = 0.11).</p><p>Specimen GIT 878-1123 is a fragment of a mature body chamber and eight chambers of the phragmocone (Fig. 40C, G). In this specimen, the ontogenetic change of the suture shape is well seen. At a conch height of ca 37 mm, the sutures are nearly straight and 5 mm distant (RCL = 0.14) and ca 20 mm further adorally the sutures form shallow lateral lobes, and are only 2–3 mm apart. The preserved part of the phragmocone is nearly tubular and straight. The siphuncular segments are expanded within the chambers and wide. Endosiphuncular bullettes deposits occur which protract in apical direction from the septal necks (Fig. 37F).</p><p>Comparison</p><p>This species of Kiaeroceras differs from all other species of the genus in having a small adult size of less than 40 mm conch height at the base of the mature body chamber.</p></div>	https://treatment.plazi.org/id/93268783961C704DFD9DFEB1FC4AFBBC	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783961D704AFDB8FB38FEA3FB7E.text	93268783961D704AFDB8FB38FEA3FB7E.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Kiaeroceras ormsoense Strand 1934	<div><p>Kiaeroceras (?) ormsoense sp. nov.</p><p>urn:lsid:zoobank.org:act: DF10785E-0267-4AD5-B8E6-90B2BBD9EA1F</p><p>Figs 35F, H, 37D</p><p>Diagnosis</p><p>Kiaeroceras with CHI of ca one, and an adult body chamber with a height of ca 50 mm, which is nearly as long as high.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Vormsi Island, Saxby shore (N); Kõrgessaare Formation, Vormsi Regional Stage; GIT 878- 63.</p><p>Description</p><p>The holotype is a fragment of the phragmocone and a mature body chamber (Fig. 35F, H). Parts of the outer shell are preserved, which show that the shell was apparently smooth or was ornamented with fine irregularly spaced growth lines. At the base of the body chamber, the conch height is 52 mm and the CHI nearly 1. In cross section, the margin on the prosiphuncular side is narrower than the opposite margin. The body chamber is 52 mm long and at the aperture 54 mm in diameter. The peristome is only partially preserved and where visible is simple and directly transverse. In lateral view, the body chamber is straight with straight or very slightly convex dorsal and ventral conch margins. The phragmocone is slightly curved endogastrically. The sutures are directly transverse and straight. The adoral-most sutures are crowded, indicate maturity of the specimen. At a conch height of 42 mm, the phragmocone is 39 mm wide (CHI = 1.07), and 30 mm further adorally, the height is 31 mm (angle of expansion = 21°). The septa are 4 mm apart where the conch height is 40 mm (RCL = 0.1). The siphuncle is strongly expanded within the chamber in lateral view, wider near the adapical surface of the septa with a maximum height of 8 mm where the septal foramen is 6 mm the chamber length is 4 mm, and the conch height is 40 mm (RSH = 0.15, RSS = 1.33, SCR = 2). There, the distance of the septal foramen from the conch margin is 2 mm. The connecting ring is thick and thick endosiphuncular bulletes occur. The septal necks are cyrtochoanitic (Fig. 37D).</p><p>Remarks</p><p>This specimen is placed with question mark into Kiaeroceras because it differs from other members of the genus in having a circular conch cross section, a wider angle of expansion, resulting also in a slightly bulged mature body chamber, and it is slightly endogastrically curved. Its gross morphology is intermediary between typical members of Diestoceras and Kiaeroceras . It differs from the former in having a slender shell and a relatively elongate body chamber. The erection of a new genus for this species must wait until more material is known, especially from the apical parts of Kiaeroceras, which is mostly known from isolated mature body chambers. Herein, this species is placed within Kiaeroceras because it fits the existing (relatively broadly defined) diagnosis of this genus (see above).</p><p>The siphuncular structure, and in particular the actinosiphonate deposits of Diestoceras are poorly known. Flower &amp; Teichert (1957: 42) discuss the possibility that the actinosiphonate deposits seen in some species of the genus are modified bullettes, which would mean that it should be transferred to the Discosorida . This species, being intermediate between Kiaeroceras and Diestoceras could support this hypothesis.</p><p>Comparison</p><p>The species is unique to the genus in having a CHI of nearly one and a slightly inflated mature body chamber.</p></div>	https://treatment.plazi.org/id/93268783961D704AFDB8FB38FEA3FB7E	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783961A704AFD96FB7AFB22F837.text	93268783961A704AFD96FB7AFB22F837.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Kiaeroceras ormsoense Strand 1934	<div><p>Kiaeroceras (?) cf. ormsoense</p><p>Fig. 35J</p><p>Material examined</p><p>ESTONIA • 1 spec.; Vormsi Island, Saxby shore (N); Kõrgessaare Formation, Vormsi Regional Stage; TUG 1680-20 .</p><p>Description</p><p>Specimen TUG 1680-20 is a slightly endogastrically curved fragment of a mature body chamber and four chambers of the phragmocone. The conch surface is apparently smooth. At the base of the body chamber the conch height is 47 mm. The body chamber is 52 mm long, with parts of the peristome preserved. In lateral view, the dorsal and ventral margins of the body chamber are straight. The preserved part of the phragmocone is 20 mm long and increases in height from 43 mm to 47 mm (angle of expansion = 11°). At its adapical end, the conch width is 40 mm (CHI = 1.08). There, the conch cross section is elliptically rounded. The sutures are directly transverse and 6 mm apart where the conch height is 45 mm (RCL = 0.13)</p><p>Remarks</p><p>The specimen is similar in conch shape, suture spacing, suture shape and siphuncular shape and position to K. (?) ormsoense sp. nov. but differs from this species in angle of expansion and mature size. More material is needed to evaluate the interspecific variability in mature size among specimens of K. (?) ormsoense in order to establish a new species for the two specimens described above.</p></div>	https://treatment.plazi.org/id/93268783961A704AFD96FB7AFB22F837	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783961B704BFD9DFEB1FB6FF8BC.text	93268783961B704BFD9DFEB1FB6FF8BC.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Kiaeroceras urgense Kröger 2025	<div><p>Kiaeroceras urgense sp. nov.</p><p>urn:lsid:zoobank.org:act: 4B0FA1B5-E540-4E9C-B93B-AEC7648EF1A2</p><p>Figs 31B, 35I</p><p>Diagnosis</p><p>Kiaeroceras with CHI of ca 1.1, a relatively long mature body chamber (RBL ca 1.7) and a mature conch height of ca 50 mm.</p><p>Etymology</p><p>Referring to the type locality.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Urge quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 103-75.</p><p>Paratypes</p><p>ESTONIA • 2 specs; Hiimuaa Island, Paluküla quarry; Moe Formation, Pirgu Regional Stage; TAM G136:33, TAM G432:727 • 1 spec.; same data as for preceding; TUG 47-864 .</p><p>Description</p><p>The holotype (Fig. 35I) is a relatively well-preserved part of a nearly complete mature body chamber and phragmocone. The conch surface is nearly smooth, ornamented with partly distinct, irregularly spaced growth lines or rugae (Fig. 31B). At the base of the body chamber, the conch height and width are 48 mm and 45 mm, respectively (CHI = 1.07). Hence, the conch cross section is slightly compressed. At the aperture, the conch cross section is not fully preserved, and a measurement of the conch width is not possible. The apertural height is 52 mm. With its total length of ca 80 mm, the body chamber is nearly tubular and straight. In cross section, the prosiphuncular side is more narrowly rounded, drop-shaped. In lateral view, the margins are almost straight.</p><p>The phragmocone is slightly endogastrically curved with a conch height increasing from 36 mm to 47 mm over a length of 60 mm (angle of expansion = 11°). A conspicuous constriction occurs at ca 30 mm adapically of the base of the body chamber with a conch height of ca 38 mm. At the adapical end of the specimen, the conch height is 33 mm, the corresponding width is 32 mm. The sutures are nearly transverse at the adapical end of the specimen and with shallow lateral lobes near the base of the mature body chamber. The septal foramen is close to the conch margin on the concave side of the conch. It has a diameter of ca 3 mm (RSH = 0.09). Traces of expanded siphuncular segments are preserved.</p><p>A second specimen (TUG 47-864) is a poorly preserved, slightly curved, fragment of a phragmocone and body chamber with a length of ca 130 mm of which only half of the conch is preserved. The siphuncle is missing, and the septa are fragmentary. The conch, however, shows the irregular constrictions of the phragmocone present in the holotype. The base of the body chamber has a height of 44 mm. The conch height expands with angles of expansion between 13° (heights 37 mm to 42 mm) and 22° (heights 30 mm to 37 mm).</p><p>Comparison</p><p>This species has a smaller adult size than K. frognoyense (mature body chamber height 68 mm), it has a less compressed conch cross section than K. heryoense Strand, 1934 (CHI = 1.15), and a longer body chamber than K. (?) ormsoense sp. nov. (mature body chamber height = 54 mm, RBL = 1).</p></div>	https://treatment.plazi.org/id/93268783961B704BFD9DFEB1FB6FF8BC	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396187048FD40FEB1FDE5FBD1.text	9326878396187048FD40FEB1FDE5FBD1.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Kiaeroceras undefined-A	<div><p>Kiaeroceras sp. A</p><p>Fig. 40A, D</p><p>Material examined</p><p>ESTONIA • 1 spec.; Hiumaa Island, Kõrgessaare quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 895-69 .</p><p>Description</p><p>The specimen is a fragment of a mature body chamber and phragmocone. The conch height and width at the base of the body chamber are 41 mm and 37 mm, respectively (CHI = 1.1). The conch is nearly straight. The conch cross section is elliptical. The length of the body chamber is not fully preserved, it was longer than 37 mm. In lateral view, margins of the body chamber are slightly convex; the body chamber reaches its greatest height of 42 mm ca 23 mm from the base. At the base of the body chamber, a ca 3 mm thin band of oncomyarian muscle scars is preserved. Five chambers of the phragmocone are preserved, indicating a low angle of expansion, which cannot be measured because of the incomplete preservation. Septal crowding of the adoral-most septa indicates maturity of the specimen. The sutures form very shallow lateral lobes. The siphuncle is located close to the conch margin and expands between the septal foramens toward a width of ca 5 mm. The width of the septal foramen is ca 4 mm where the conch height is 38 mm (RSH = 0.11, RSS = 1.25), and the septal distance is 5 mm (RCL = 0.13, SCR = 1).</p><p>Remarks</p><p>This fragment differs from K. kaebliki sp. nov. in its larger in adult size, and less compressed, more equally rounded conch cross section.</p></div>	https://treatment.plazi.org/id/9326878396187048FD40FEB1FDE5FBD1	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396187048FD5FFBE3FB8EF8E7.text	9326878396187048FD5FFBE3FB8EF8E7.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Kiaeroceras undefined-B	<div><p>Kiaeroceras sp. B</p><p>Fig. 35A–B</p><p>Material examined</p><p>ESTONIA • 1 spec.; Vormsi Island, Saxby shore; Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-161 .</p><p>Description</p><p>The specimen is an almost tubular, almost straight fragment of a mature body. The conch surface is poorly preserved but apparently smooth. The conch cross section is drop-shaped with a widely rounded antisiphuncular and a narrower prosiphuncular side. The conch height and width are 43 mm and 37 mm, respectively (CHI = 1.4). The body chamber is 63 mm long, without constriction. The remaining peristome appears to be straight and directly transverse. The base of the body chamber indicates that the sutures formed shallow lateral lobes. The siphuncle is nearly marginal, and the septal foramen has a width of 4 mm (RSH = 0.09).</p><p>Remarks</p><p>The fragment is relatively strongly compressed compared with other Estonian specimens of Kiaeroceras . Its adult body chamber height is smaller than in the Norwegian species.</p></div>	https://treatment.plazi.org/id/9326878396187048FD5FFBE3FB8EF8E7	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396187049FD5FF891FE60FD5D.text	9326878396187049FD5FF891FE60FD5D.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Kiaeroceras undefined-C	<div><p>Kiaeroceras sp. C</p><p>Fig. 35E, G</p><p>Material examined</p><p>ESTONIA • 1 spec.; Niibi hillock; Moe Formation, Pirgu Regional Stage; GIT 225-997 .</p><p>Description</p><p>The specimen is a nearly complete mold of a mature body chamber with height, width, and length of 53 mm, 44 mm and 75 mm, respectively (CHI = 1.11). The conch is straight and tubular. The conch cross section is oval compressed with a relatively narrow, drop-shaped margin on the prosiphuncular side. The peristome is nearly straight and a very shallow (5 mm) hyponomic sinus occurs on the prosiphuncular side. The siphuncle is nearly marginal with a septal foramen ca 8 mm in diameter, located ca 3 mm from the conch margin (RSH = 0.15, RSP = 0.16).</p><p>Comparison</p><p>This specimen differs from K. ormsoense sp. nov., to which it is otherwise similar, in having a compressed conch cross section and a longer, perfectly tubular body chamber (RBL = 1.4 as compared with RBL ca 1 in K. (?) ormsoense).</p></div>	https://treatment.plazi.org/id/9326878396187049FD5FF891FE60FD5D	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396197049FD5FFD67FAE4FB1F.text	9326878396197049FD5FFD67FAE4FB1F.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Kiaeroceras undefined-D	<div><p>Kiaeroceras sp. D</p><p>Fig. 40B, E</p><p>Material examined</p><p>ESTONIA • 1 spec.; Kärdla quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 1745-201 .</p><p>Description</p><p>The specimen is a fragment of a very slightly endogastrically curved mature body chamber with conch height, and width at its base of 61 mm and 49 mm, respectively (CHI = 1.44). The preserved part of the body chamber is 65 mm long and tubular in lateral view. The conch cross section is oval with a narrower prosiphuncular side. The siphuncle is close to the conch margin and ca 7 mm wide (RSH = 0.11).</p><p>Remarks</p><p>In its dimensions, this specimen is most similar to the Norwegian species of Kiaeroceras but differs in having a more compressed conch ( K. frognoyense has a CHI of 1.15, and K. heroyense a CHI of 1.25).</p></div>	https://treatment.plazi.org/id/9326878396197049FD5FFD67FAE4FB1F	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396197056FD40FA98FD7FFE8C.text	9326878396197056FD40FA98FD7FFE8C.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Kiaeroceras undefined-E	<div><p>Kiaeroceras sp. E</p><p>Figs 37A, 40F</p><p>Material examined</p><p>ESTONIA • 1 spec.; Vormsi Island, Saxby shore (N); Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-21 .</p><p>Description</p><p>The specimen is a fragment of a mature body chamber and nine chambers of the phragmocone (Fig. 40F). The body chamber is straight and tubular with a conch height of ca 48 mm. The phragmocone is slightly endogastrically curved. The adoral-most two septa are crowded. The phragmocone increases in height from 44 mm to 47 mm at a length of 34 mm (angle of expansion = 5°). The sutures are directly transverse and straight. The siphuncle is near the conch margin, its segments are strongly expanded within the chambers with a height of 8 mm where the conch height is 46 mm, and the chamber length is 5 mm (SCR = 1.6). The septal necks are cyrtochoanitic. Endosiphuncular bullettes occur (Fig. 37A).</p><p>Remarks</p><p>The specimen is similar to K. urgense sp. nov. with respect to the low angle of expansion of the phragmocone and the size and shape of the mature body chamber. It differs from the former in lacking the constriction at the phragmocone and in having a smaller angle of expansion. It cannot fully be compared with other species of the genus because the conch cross section is not preserved, and the specimen is therefore left in open nomenclature.</p></div>	https://treatment.plazi.org/id/9326878396197056FD40FA98FD7FFE8C	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396067056FDC6FE29FB2FFAE3.text	9326878396067056FDC6FE29FB2FFAE3.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Lyckholmoceras Teichert 1930	<div><p>Genus Lyckholmoceras Teichert, 1930</p><p>Type species</p><p>Lyckholmoceras estoniae Teichert, 1930, from Saaremõisa (Lyckholm), N of Haapsalu, Läänemaa, Estonia, Kõrgessaare Formation, Vormsi Regional Stage; by monotypy.</p><p>Emended diagnosis</p><p>Slightly endogastrically curved, large brevicones with slightly compressed conch cross section, conch margin narrower at ventral side; mature body chamber uncontracted or at mid-length, with distinct hyponomic sinus; sutures with shallow lateral lobe; siphuncle marginal with slightly expanded segments; endosiphuncular bullettes occur.</p><p>Remarks</p><p>The genus was placed within the Cyrtogomphoceratidae by Flower in Flower &amp; Teichert (1957) and without further discussion classified within the Diestoceratidae in Sweet (1964b: K295). Both families contain genera with swollen siphuncles and with annulosiphonate deposits or endosiphuncular bullettes. However, here I follow Teichert (1964b) to restrict the cyrtogomphoceratids to endogastrically curved and the diestoceratids to straight and exogastrically curved forms (see above). Hence, Lyckholmoceras is interpreted as a member of the Cyrtogomphoceratidae, herein.</p><p>The original diagnosis is emended herein regarding the presence of endosiphuncular deposits. In Teichert (1930: 301) it is stated “Keine Ausfüllungen des Siphos bekannt” (translated from German: “Endosiphuncular deposits unknown”. This statement was emended by Sweet (1964b: K295) to “actinosiphonate deposits not known”. In the Estonian material, assigned to Lyckholmoceras, studied herein, endosiphuncular bullettes occur. The genus diagnosis is changed accordingly.</p></div>	https://treatment.plazi.org/id/9326878396067056FDC6FE29FB2FFAE3	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396067054FDD9FA95FD2EFE12.text	9326878396067054FDD9FA95FD2EFE12.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Lyckholmoceras norvegiae Strand 1934	<div><p>Lyckholmoceras norvegiae Strand, 1934</p><p>Figs 37G, 38A–B</p><p>Lyckholmoceras norvegiae Strand, 1934: 88–91, pl. 11 figs 1a–b, 2.</p><p>Beloitoceras heterocurvatum Strand, 1934: 77, pl. 10 fig. 11 (non pl. 10 figs 8–10).</p><p>Parryoceras strandi Sweet, 1959: 58–59, pl. 9 figs 5–6, pl. 10 fig. 6.</p><p>Lyckholmoceras norvegiae – Flower in Flower &amp; Teichert 1957: 59, text-figs c, g. ― Dzik 1984: 67, text-fig. 18.13.</p><p>Diagnosis</p><p>Lyckholmoceras with compressed conch cross section (CHI ca 1.5), in longitudinal direction moderately curved; mature body chamber almost straight with uncontracted aperture and well-marked hyponomic sinus; sutures with shallow lateral lobes; siphuncular segments slightly expanded within chambers, narrowing adorally, with SCR of ca 1; ornamented with faint, densely irregularly spaced lirae. Small endosiphuncular bullettes are present. (Compiled from Strand 1934: 89–90.)</p><p>Material examined</p><p>ESTONIA • 1 spec.; Haapsalu holm; Adila Formation, Pirgu Regional Stage; TUG 1745-2 • 4 specs; Vormsi Island, Hosholm shore (tower locality); Adila Formation, Pirgu Regional Stage; GIT 878-166, GIT 878-167, GIT 878-187, GIT 878-226 .</p><p>Description</p><p>The most complete specimen is GIT 878-226, which preserves parts of the mature living chamber and a 70 mm long mold of the phragmocone (Fig. 39A–B). The conch height cannot be measured in this specimen because the prosiphuncular side of the conch is not preserved but the preserved parts show the general conch shape. In lateral view, the body chamber appears straight, the adoral ca 35 mm of the phragmocone has a convex outline at the antisiphuncular side and the adapical part is straight. The straight part of the phragmocone has a conch width of &lt;37 mm. The conch cross section is ovally compressed with a narrow margin at the antisiphuncular side. At the base of the body chamber, the conch width is 38 mm and the height is approximately 50 mm (CHI = 1.3). The peristome is straight and simple on the antisiphuncular side. It is ca 40 mm distant from the base of the body chamber. The part of the phragmocone with width &lt;ca 35 mm is distinctly longitudinally striated; ca 60 striae occur around the circumference. The sutures are 5 mm apart where the conch width is 28 mm, they form shallow lateral lobes.</p><p>The conch cross section is preserved in specimen GIT 878-167, which is a small fragment of a phragmocone with only one chamber completely preserved. There, the conch height and width are 32 mm and 25 mm respectively (CHI = 1.28), and the conch cross section is elliptically compressed with narrow dorsal and ventral margins. The septal foramen is located ca 1–2 mm from the conch margin and has a diameter of 3 mm (RSH = 0.09, RSP ca 0.07).</p><p>The angle of expansion can be measured in specimen TUG 1745-2, which is a fragment of a phragmocone in which the conch height increases from 20 mm to 32 mm in 37 mm (angle of expansion = 18°). Specimens GIT 878-166, GIT 878-167, GIT 878-187, and TUG 1745-2 have conch heights of less than 40 mm and all show the characteristic longitudinal striation on the mold of the outer shell of the phragmocone (e.g., Fig. 38A–B).</p><p>The details of the siphuncle and septal necks are preserved in GIT 878-187 (Fig. 37G), and GIT 878- 167. In both specimens, the siphuncle is located close to the margin at the concave side of the conch. The siphuncular segments are expanded tubular. The connecting ring is relatively thick and adnate on the adapical surface of the septum on the siphuncular side nearest to the conch center and adnate at the adoral side of the septa at the siphuncular side nearest to the conch margin. Where the conch width is 32 mm, the chamber length is 4.5 mm, the maximum height of the siphuncle is 4 mm, and the septal foramen is 2 mm (GIT 878-187, RSS = 2, SCR = 0.89). The septal necks are cyrtochoanitic; they are recumbent and adnate at the side of the siphuncle nearest to the conch margin. Small bullettes occur, which expand in adapical direction.</p><p>Remarks</p><p>The specimens described above are slightly less compressed in conch cross section than the types of the species described by Strand (1934), which have a CHI of 1.36–1.49. This difference can be interpreted as taphonomic effect or as an effect of ontogenetic change in CHI and measurement at different growth stages. More material is needed to evaluate the intraspecific and ontogenetic variability of the CHI. The Estonian specimens are nevertheless placed within L. norvegiae, based on the general similarities in conch dimensions and conch shape with this species.</p><p>The specimen described under Parryoceras strandi Sweet, 1959 is identical in conch shape, dimensions, and with regard of the shape and size of the siphuncle-septal neck complex and must be synonymized with L. norvegiae . It remains an open question how the closely related Parryoceras Sweet &amp; Miller, 1957 compares in detail to Lyckholmoceras, because the details of the septal necks and connecting rings are poorly known in the former. Parryoceras euchari Sweet &amp; Miller, 1957, the type of the genus, apparently differs from species of Lyckholmoceras in having a more strongly constricted mature body chamber than species of Lyckholmoceras .</p></div>	https://treatment.plazi.org/id/9326878396067054FDD9FA95FD2EFE12	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396047054FDBFFDA6FBBCFC2D.text	9326878396047054FDBFFDA6FBBCFC2D.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Strandoceras Flower 1946	<div><p>Genus Strandoceras Flower, 1946</p><p>Type species</p><p>Protophragmoceras tyriense Strand, 1934, from Stavnestangen, Ringerike, Norway, Bønsnes Formation, Late Katian; by original designation.</p><p>Diagnosis</p><p>Endogastric cyrtocones with compressed conch cross section, ventral side of cross section more narrowly rounded than the dorsal side; mature body chamber less curved than the rest of the conch; peristome with small sinus on concave and wide sinus on convex side of conch; sutures with shallow lateral lobes slightly shifted adapically at the dorsal side; siphuncle near conch margin with broadly expanded segments and endosiphuncular bullettes. (Adopted from Flower 1946: 434.)</p></div>	https://treatment.plazi.org/id/9326878396047054FDBFFDA6FBBCFC2D	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396047052FDC8FC56FE66F953.text	9326878396047052FDC8FC56FE66F953.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Strandoceras sphynx (Schmidt 1858)	<div><p>Strandoceras sphynx (Schmidt, 1858)</p><p>Figs 31C–D, 41A, F, 42A</p><p>Phragmoceras sphynx Schmidt, 1858: 200 .</p><p>Phragmoceras sphynx – Eichwald 1860: 1272–1273. ― Roemer 1861: 61. ― Strand 1934: 93, 107. ― Flower 1946: 434. ― Flower in Flower &amp; Teichert 1957: 57, 114, text-figs 15e, g–h.</p><p>Protophragmoceras sphinx (sic) – Teichert 1930: 270, 299–301, pl. 7 fig. 20, pl. 8 fig. 24, text-figs 3–4. ― Balashov 1953a: 212. ― Dzik 1984: 48, 52, 65, text-fig. 14.5, pl. 7 fig. 7.</p><p>Diagnosis</p><p>Large Strandoceras with mature conch height of more than 70 mm; conch cross section oval compressed with narrower ventral conch margin; mature body chamber slightly endogastrically curved, up to ca 80 mm long, nearly tubular or slightly gibbous with maximum conch height near base; ornamented with fine transverse lirae.</p><p>Material examined</p><p>ESTONIA • 1 spec.; Vormsi Island; Saxby old quarry; Moe Formation, Pirgu Regional Stage; TUG 1672-29 • 1 spec.; Raplamaa, Pahkla; Moe Formation, Pirgu Regional Stage; TUG 1745-195 • 1 spec.; Läänemaa, Niibi hillock; Moe Formation, Pirgu Regional Stage; TAM G432:68 • 2 specs; Sutlepa quarry; Adila Formation, Pirgu Regional Stage; TAM G149:27, TAM G149:28 .</p><p>Type locality and horizon</p><p>Niibi, Estonia; Moe Formation, Pirgu Regional Stage.</p><p>Description</p><p>Specimen TUG 1672-29 is a nearly complete endogastrically curved conch preserving the outer shell and part of the mature body chamber (Figs 31D, 41A). The conch surface is ornamented with slightly irregularly spaced, distinct growth bands and / or lirae, which are adapically shifted at the antisiphuncular side of the conch curvature, and which form a hyponomic sinus on the prosiphuncular side. The conch cross section is preserved only at the apical end of the specimen. There, the conch height and width are 17 mm and 15 mm, respectively (CHI = 1.13) and the cross section oval compressed with a narrow margin on the prosiphuncular side. In lateral view, the antisiphuncular conch margin is convex throughout the entire length, the prosiphuncular conch margin is concave in early growth stages and straightens at a position where the conch height is ca 55–60 mm, resulting in an overall inflated conch shape. The conch reaches a maximum height of ca 72 mm at ca 55 mm from the peristome, adorally of which, the conch height decreases to ca 68 mm at the peristome (Fig. 42A; supplementary data 4). The conch is also inflated in width, although, the extent of the inflation cannot be measured in this or other available specimens. The angles of expansion reach a maximum with ca 27° between conch heights of 17 mm and 25 mm.</p><p>Where visible, the sutures are straight and directly transverse on the lateral sides and form deep narrow saddles on the prosiphuncular side; they are 7 mm apart where the conch height is 37 mm (RCL = 0.19).</p><p>Another nearly complete specimen is TAM G432:68 (Figs 31C, 41F). This specimen is similarly ornamented to specimen TUG 1672-29 (Fig. 31D). The conch cross section is not preserved. In lateral view, the antisiphuncular conch margin is convex throughout the entire length, the prosiphuncular conch margin is concave in early growth stages and straightens at a position where the conch height is ca 65 mm, resulting in an overall bulged conch shape. The conch reaches a maximum height of ca 73 mm at ca 55 mm from the peristome. Adorad of this, the conch height decreases toward ca 70 mm at the peristome. The conch is also inflated in width. The angles of expansion reach a maximum of ca 37° between conch heights of 31 mm and 43 mm. The sutures are straight and directly transverse on the lateral sides and are 11 mm apart where the conch height is 52 mm (RCL = 0.21). At the base of the body chamber, the conch height is 70 mm. The body chamber has a length of ca 80 mm and is only faintly curved.</p><p>Remarks</p><p>In the Lyckholm strata, at least three relatively similar species of Strandoceras occur ( S. sphynx, S. kalevipoegi sp. nov., and S. sulevipoegi sp. nov.). Schmidt’s (1858: 200) original description does not allow to specify, which of the three species he referred to. Possibly, Schmidt (1858), more generally referred to the slender morphotype of Strandoceras, which these three species represent, but a lectotype designation is not possible because the Schmidt type-material could not be identified. The slender morphotype is also figured in Teichert (1930) under this species (see list of synonymy). For simplicity, it is suggested here, that this slender morphotype is synonymized with S. sphynx .</p><p>Comparison</p><p>Strandoceras kalevipoegi sp. nov. is larger (conch height ca 80 mm), and more strongly curved. Strandoceras tyriense (Strand, 1934) and S. sulevipoegi sp. nov. is smaller (conch heights are ca 55 mm and 65 mm, respectively) and has a lower angle of expansion during late ontogeny. Strandoceras schmidti (Teichert, 1930) and S. muhvi sp. nov. differ in having a shorter, more rapidly enlarging conch (compare in Fig. 42A–B).</p></div>	https://treatment.plazi.org/id/9326878396047052FDC8FC56FE66F953	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396027050FDA1F964FD48FCB7.text	9326878396027050FDA1F964FD48FCB7.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Strandoceras kalevipoegi Kröger 2025	<div><p>Strandoceras kalevipoegi sp. nov.</p><p>urn:lsid:zoobank.org:act: 23EA0987-FD52-4193-98AA-54A085118FB8</p><p>Fig. 41E, 42A</p><p>Diagnosis</p><p>Large Strandoceras reaching conch heights of 80 mm; phragmocone strongly endogastrically curved with angle of expansion of up to 35°; mature body chamber ca 80 mm long, contracted, and nearly straight with greatest height at the adapical half of its length; conch surface smooth or with very fine growth lines.</p><p>Etymology</p><p>From Kalevipoeg, the main hero in the Estonian national epic, Friedrich R. Kreutzwaldʼs (1803–1882) poem ”Kalevipoeg”, referring to the large size of this species.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Kohila quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 42-431.</p><p>Paratypes</p><p>ESTONIA • 2 specs; Vormsi Island, Saxby shore (S); Kõrgessaare Formation, Vormsi Regional Stage; TUG 899-54, TUG 899-89 • 1 spec.; Sutlepa quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 80-509 .</p><p>Description</p><p>The holotype is a fragment of parts of an endogastrically curved phragmocone and a mature body chamber, partly preserving the outer shell. The conch surface is preserved near the base of the peristome, where it is smooth or with very fine growth lines, only. In lateral view, the conch margin at the antisiphuncular side is convex throughout the entire length. The prosiphuncular side of the conch margin is concave on the phragmocone and nearly straight on the body chamber. At the base of the body chamber, the conch height is 75 mm. The greatest conch height of 80 mm is located in the lower part of the body chamber, ca 30 mm from its base. The body chamber is ca 80 mm long. The conch cross section of the specimen is not preserved but it was apparently compressed with an oval shape, slightly narrower on the prosiphuncular side with a reconstructed CHI of ca 1.6 at the base of the body chamber. The phragmocone expands with an angle of expansion of up to 14°at conch heights between 62 mm and 72 mm. The sutures form very shallow lateral lobes and distinct narrow saddles on the prosiphuncular side of the conch; they are ca 9 mm apart where the conch height is 72 mm (RCL = 0.13). The peristome is straight and simple with a deep (ca 15 mm) hyponomic sinus on the prosiphuncular side.</p><p>The more strongly curved apical sections of the phragmocone are preserved in specimen TUG 899-89. The conch cross section is oval compressed with a narrower margin on the prosiphuncular side. The conch height and width are 36 mm and 32 mm, respectively (CHI = 1.13). The conch expands with an angle of expansion of 35° between conch heights 33 mm and 49 mm.</p><p>The details of the siphuncle and the septal necks are well-preserved in specimen TUG 80-509. There, the siphuncle is marginal, the septal foramen has a width of 9 mm, the siphuncular segments expand to 15 mm in height, and the chamber length is 5 mm, where the conch height is 66 mm (RSH = 0.14, RSS = 0.6, SCR = 3). The septal necks are cyrtochoanitic and thick endosiphuncular bullettes are present.</p><p>Comparison</p><p>This species is unique among Strandoceras in reaching adult conch heights of 80 mm, in having a nearly smooth conch surface, and in having a long, nearly straight mature body chamber, which contrasts with the curved rapidly expanding phragmocone.</p></div>	https://treatment.plazi.org/id/9326878396027050FDA1F964FD48FCB7	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
932687839600705EFDACFCC1FE0BFEA2.text	932687839600705EFDACFCC1FE0BFEA2.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Strandoceras kohilense Kröger 2025	<div><p>Strandoceras kohilense sp. nov.</p><p>urn:lsid:zoobank.org:act: 8C055DE8-1F47-4517-8965-EA9C4D8E8EF5</p><p>Figs 43C, 44B</p><p>Diagnosis</p><p>Strandoceras with drop-shaped conch cross section, narrower at the dorsal conch margin; mature body chamber nearly tubular in shape, slightly curved with maximum conch height of ca 50 mm; distinct hyponomic sinus on concave conch margin.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Kohila quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 47-883.</p><p>Paratypes</p><p>ESTONIA • 2 specs; Vormsi Island, Saxby shore; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-1136, GIT 878-79 .</p><p>Description</p><p>The most complete specimen is TUG 47-883 (Fig. 44C), which is an endogastrically curved fragment of a mature body chamber and four chambers of the phragmocone. The conch surface is not preserved. At the base of the body chamber the height and width are ca 47 mm and 27 mm, respectively (CHI = 1.74), and the elliptically compressed conch cross section has narrow dorsal and ventral margins. The specimen is probably slightly deformed (compressed). The body chamber is in its length of 47 mm completely preserved (RBL = 1). At the aperture, a distinct hyponomic sinus is present on the prosiphuncular side. In lateral view, the prosiphuncular margin is concave and the antisiphuncular margin convex, resulting in a curved tubular shape of the mature body chamber. The angle of expansion of the phragmocone near the base of the body chamber is low (3°), increasing in height between 46 mm and 47 mm at a length of 18 mm. The sutures form shallow lateral lobes and distinct, narrow saddles near the location of the siphuncle; they are 7 mm apart where the conch height is 47 mm (RCL = 0.15). The siphuncle and the septal foramen are too poorly preserved to be measured. The position of the siphuncle is nearly marginal.</p><p>Specimen GIT 426-1136 is a fragment of four chambers of the phragmocone and a mature body chamber of nearly identical to TUG 47-883. It is less deformed, and details of the septal foramen are better preserved. At the base of the body chamber, the height and width are 48 mm and 35 mm, respectively (CHI = 1.37). The body chamber is 47 mm long, curved and nearly tubular in lateral view. The sutures form wide lateral lobes and narrow, distinct saddles at the location of the siphuncle, they are 7 mm apart where the conch height is 50 mm (RCL = 0.14). The septal foramen is near the conch margin.</p><p>The details of the siphuncle and septal neck are preserved in specimen GIT 878-79 (Fig. 44B). At a conch height of 47 mm, a chamber is 6 mm long, the septal foramen in 4.5 mm high, and the siphuncular segments expand toward a height of 9 mm (RSH = 0.1, RSS = 2, SCR = 1.5). The connecting ring is thin, and the septal necks are cyrtochoanitic. Simple, small endosiphuncular bullettes are present. The connecting ring is hyposeptally adnate.</p><p>Remarks</p><p>The adult size of S. kohilense sp. nov. (mature conch height ca 50 mm) is smaller than in S. kalevipoegi sp. nov., S. sphynx, S. sulevipoegi sp. nov., S. tyriense, and S. muhvi sp. nov. The species S. schmidti differs from S. kohilense in having a wider angle of expansion. Strandoceras kohilense differs from the other species in having at the base of the mature body chamber, a drop-shaped conch cross section with a margin which is narrower at the dorsal side than on the ventral side. This difference could suffice to erect a new genus. However, nothing is known about the ontogenetic change of the conch cross section in this species, and it cannot be ruled out that the conch cross section is slightly deformed by taphonomic processes. More material is needed to evaluate the differences between this species and the type species of Strandoceras .</p></div>	https://treatment.plazi.org/id/932687839600705EFDACFCC1FE0BFEA2	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783960E705FFD9FFED5FA8AFB99.text	93268783960E705FFD9FFED5FA8AFB99.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Strandoceras muhvi Kröger 2025	<div><p>Strandoceras muhvi sp. nov.</p><p>urn:lsid:zoobank.org:act: 06217430-05D8-4FDB-829D-06E6E44D3E05</p><p>Figs 41C, 42B, 44A</p><p>Diagnosis</p><p>Short Strandoceras with angle of expansion of up to ca 40°; conch cross section elliptically compressed; maximum conch height ca 65 mm; mature body chamber ca 70 mm long, slightly curved and contracted; ornamented with fine transverse lirae and / or growth bands.</p><p>Etymology</p><p>Refers to Muhv, a small troll in Eno Raud’s (1928–1996) children-book series “Naksitrallid”.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Kohila quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 42-432.</p><p>Paratypes</p><p>ESTONIA • 1 spec.; Vormsi Island, Saxby shore; Kõrgessaare Formation, Vormsi Regional Stage; TUG 939-58 • 1 spec.; same data as for preceding; GIT 878-27 .</p><p>Description</p><p>The most complete specimen is TUG 42-432 (Fig. 41C), which preserves parts of the phragmocone of the adult body chamber, and part of the outer shell. The conch surface is poorly preserved. Near the peristome, traces of transverse lirae or growth bands occur, which are ca 2 mm apart. The complete conch cross section is only preserved at the adapical end. There, the conch height and width are 29 mm and 27 mm, respectively (CHI = 1.07) and it is rounded elliptical in shape. At the base of the body chamber, the conch width can be reconstructed. There, the height and width are 67 mm and 54 mm, respectively (CHI = 1.25). In lateral view, the antisiphuncular margin is convex throughout. The prosiphuncular conch margin is only preserved in the phragmocone, which is concave throughout but with a lower curvature than the antisiphuncular conch margin, resulting in an inflated conch shape with a maximum conch height of ca 65 mm reached at ca 60 mm from the peristome. The complete length of the body chamber is ca 70 mm (RBL = 1.04). The phragmocone expands with an angle of 14°–41° with a maximum reached at conch heights of 41–50 mm (see supplementary data 1 for measurements). The sutures are straight and directly transverse and shallow and narrow, but distinct saddles occur on the prosiphuncular side. Throughout the preserved part of the phragmocone, the sutures are 5–7 mm apart (RCL: 0.12–0.17).</p><p>Details of the siphuncle and septal necks are preserved in specimen TUG 939-58 (Fig. 44A).The siphuncle is marginal in position, with a wide septal foramen (ca 9 mm) where the conch height is ca 50 mm (RSH = 0.18). The maximum width of the siphuncle is 15 mm where the chamber length is 4 mm (RSS = 1.7, SCR = 3.75). Thick endosiphuncular bullettes occur. The septal necks are cyrtochoanitic.</p><p>Remarks</p><p>This species of Strandoceras is unique to the genus regarding its high angle of expansion. S. schmidti (Teichert, 1930) differs in having a less expanded conch and a smaller adult size (see below).</p></div>	https://treatment.plazi.org/id/93268783960E705FFD9FFED5FA8AFB99	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783960F705CFDC1FB1BFAFCFB27.text	93268783960F705CFDC1FB1BFAFCFB27.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Strandoceras schmidti (Teichert 1930)	<div><p>Strandoceras schmidti (Teichert, 1930)</p><p>Fig. 42B, 43B</p><p>Codoceras schmidti Teichert, 1930: 297, pl. 8 figs 25–26.</p><p>Codoceras schmidti – Strand 1934: 88. ― Miller &amp; Youngquist 1947: 13. ― Balashov 1953a: 207. ― Barskov 1972: 66.</p><p>Strandoceras schmidti – Flower in Flower &amp; Teichert, 1957: 57.</p><p>Diagnosis</p><p>Small, short Strandoceras with angle of expansion of up to ca 35°; conch cross section oval compressed, narrower at ventral side; maximum conch height ca 55 mm; mature body chamber slightly curved and contracted; ornamented with fine transverse lirae.</p><p>Material examined</p><p>ESTONIA • 1 spec.; Salu; Pirgu Regional Stage; TUG 1745-25 • 1 spec.; Lääne-Virumaa, Tapa; Moe Formation, Pirgu Regional Stage; GIT 426-440 .</p><p>Type locality and horizon</p><p>Kose-Uuemõisa, Harju county, Estonia; Vormsi–Pirgu regional stages (“Lyckholm Stufe” of Teichert 1930).</p><p>Description</p><p>TUG 1745-25 is a fragment of an endogastrically curved phragmocone and body chamber with parts of the outer shell preserved (Fig. 43B). The conch surface is nearly smooth, ornamented only with fine growth lines or growth bands. At the apical end of the specimen, the conch cross section is preserved; it is oval compressed with a narrower margin on the prosiphuncular side, with a conch height and width of 26 mm and ca 24 mm, respectively (CHI = 1.13). The conch height expands with an angle of ca 36° between conch heights of 25 mm and 46 mm. At the base of the body chamber, the conch height is 54 mm. The preserved part of the body chamber is 50 mm long. In lateral view, the antisiphuncular margin is convex throughout the entire length of the conch. The conch margin of the prosiphuncular side is preserved only on the phragmocone and the basal ca 15 mm of the body chamber, it is concave throughout, but straightens adorally. The sutures are straight and directly transverse, 5 mm apart, where the conch height is 34 mm (RCL = 0.15).</p><p>The second specimen is less well-preserved, and reliable measurements of angle of expansion and CHI are not possible. The base of the body chamber at this specimen has a height of 43 mm.</p><p>Remarks</p><p>The type specimen figured in Teichert (1930: pl. 8 figs 25–26), is incompletely preserved, not allowing for a quantification of the angle of expansion, and measurements are not given in Teichert (1930). The diagnosis given herein, therefore, is based on the material described herein combined with the original descriptions in Teichert (1930). A specimen from the Eichwald collection of St Petersburg is described and figured as “ Strandoceras oryx (Eichwald, 1861) ” (sic) in Kiselev (1991), referring to Phragmoceras oryx Eichwald, 1857 . This specimen, collected from an unspecified locality at Hiiumaa, is similar to S. schmidti (Teichert, 1930) in general shape and size. It is therefore possible that S. schmidti (Teichert, 1930) is a subjective junior synonym of Phragmoceras oryx Eichwald, 1857, and that the specimens described herein under S. schmidti should be better placed within Eichwald’s (1857) species. However, because the Eichwald material is currently inaccessible, this problem needs to be solved in a future work.</p></div>	https://treatment.plazi.org/id/93268783960F705CFDC1FB1BFAFCFB27	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783960C705DFDA2FB51FE4BF943.text	93268783960C705DFDA2FB51FE4BF943.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Strandoceras sulevipoegi Kröger 2025	<div><p>Strandoceras sulevipoegi sp. nov.</p><p>urn:lsid:zoobank.org:act: 8846BE74-EF9D-437F-B22A-493CB44C1E89</p><p>Figs 31E, 41B, D, 42A, 43A</p><p>Diagnosis</p><p>Strandoceras with relatively slender conch; angle of expansion up to 34°; mature body chamber nearly tubular, slightly endogastrically curved, ca 60–65 mm high and 75 mm long, with an oval compressed conch cross section (CHI ca 1.3) with a narrower prosiphuncular conch margin; ornamented with fine transverse lirae.</p><p>Etymology</p><p>From Sulevipoeg, a hero in the Estonian national epic, Friedrich R. Kreutzwald’s (1803–1882) poem “Kalevipoeg”, a friend of Kalevipoeg. See Strandoceras kalevipoegi sp. nov.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Salu; Pirgu Regional Stage; TUG 1745-209.</p><p>Paratypes</p><p>ESTONIA • 1 spec.; same data as for holotype; TUG 1745-209 • 1 spec.; Förby shore; Pirgu Regional Stage; TUG 1745-176 • 1 spec.; Niibi quarry; Moe Formation, Pirgu Regional Stage; TUG 42-433 • 1 spec.; Paluküla quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-565 • 1 spec.; Salutaguse; Moe Formation, Pirgu Regional Stage; TUG 1745-292 • 1 spec.; Saxby old quarry; Moe Formation, Pirgu Regional Stage; TUG 1745-198 • 1 spec.; Saxby shore; Kõrgessaare Formation, Vormsi Regional Stage; TUG 899-55 • 1 spec.; Sutlepa quarry; Adila Formation, Pirgu Regional Stage; TAM G149:26 • 1 spec.; Tapa; Moe Formation, Pirgu Regional Stage; GIT 426-48 • 1 spec.; same data as for preceding; TUG 1239-6 • 1 spec.; Vormsi Island; Vormsi–Pirgu regional stages; TUG 42-399 .</p><p>Description</p><p>Only relatively incomplete fragments are known from this species. They differ from other species of this genus in being more slender. The most complete outline of the relatively weak conch curvature is preserved in specimen TUG 42-399 (Fig. 41D), which is a fragment of the mature body chamber and eight chambers of the phragmocone, but in which the internal characters and the conch width are not preserved. The mature body chamber is preserved in six specimens with conch heights of 62–64 mm (TUG 42-399, TUG 899-55, TUG 1745-176, GIT 426-565, and widths of 48 mm (TUG 899-55, TUG 1239-6) at their bases (CHI = 1.3). The conch cross section is oval with a narrower prosiphuncular conch margin. The total length of the mature body chamber is 75 mm (TUG 42-399, TUG 899-55, TUG 1745- 176) (see Fig. 43A). The mature body chamber is slightly endogastrically curved and in lateral view has a convex margin at the antisiphuncular side and a concave margin on the prosiphuncular side. The conch height at the mature aperture is ca 65 mm (specimen TUG 1745-176).</p><p>The holotype is a fragment of a phragmocone with a length of ca 140 mm, preserving its relatively weak curvature and low angle of expansion which is 22° between conch heights of 28 mm and 33 mm, and 32° between conch heights of 33 mm and 44 mm (Fig. 41B). The outer shell is preserved in the holotype. It is ornamented with fine transverse lirae or growth bands, similar to those present in S. sphynx, but coarser (Fig. 32E). The sutures form shallow lateral lobes, and are 8 mm apart where the conch height is 35 mm (RCL = 0.23). The siphuncle is marginally positioned at the concave side of the conch curvature (endogastric curvature) with widely expanded segments. The width of the septal foramen is ca 6 mm, the width of the siphuncular segment 14 mm, and the chamber length 8 mm where the conch height is ca 50 mm (RSH = 0.12, RSS = 2.3, SCR = 1.75).</p><p>Specimen TUG 42-433 is a relatively complete fragment of a phragmocone without outer shell preserved which permits measurement of the trajectory of the angle of expansion (Fig. 42A); it expands with a minimum angle of 3° between conch heights of 60 mm and 61 mm and a maximum angle of 31° between conch heights of 37 mm and 48 mm.</p><p>Comparison</p><p>This is a relatively slender Strandoceras . The conch height at the base of the mature body chamber is 60–65 mm, which is considerably smaller than in S. kalevipoegi sp. nov. with a conch height of ca 75 mm, and in S. sphynx, which measures ca 70 mm at the base of the body chamber. Strandoceras tyriense is smaller (conch height at base of mature body chamber is ca 55 mm) and its phragmocone is more strongly curved.</p></div>	https://treatment.plazi.org/id/93268783960C705DFDA2FB51FE4BF943	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783960D705AFDCEF975FCA6FC34.text	93268783960D705AFDCEF975FCA6FC34.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	undefined-A Flower 1950	<div><p>Discosorida fam., gen. et sp. indet. A</p><p>Fig. 45A–B</p><p>Material examined</p><p>ESTONIA • 3 specs; Vohilaid Island, Vohilaid shore (E); Adila Formation, Pirgu Regional Stage; GIT 878-188 to GIT 878-190 • 1 spec.; Salu; Pirgu Regional Stage; TUG 1745-26 .</p><p>Description</p><p>All four specimens are isolated, endogastrically curved mature body chambers, without phragmocone parts. They are identical in size and shape. At the base, their height is 44–45 mm, at the aperture the height measures 36–37 mm, and the total length from base to aperture is ca 50 mm. The three specimens from Vohilaid Island are likely to be slightly deformed (compressed) with a width of ca 29 mm at the body chamber base (CHI = 1.5). In specimen TUG 1745-26, the width is 30 mm where the height is 42 mm (CHI = 1.4). The conch cross section is rounded elliptical at mid body chamber position. At the base of the body chamber, the antisiphuncular margin is more narrow, almost rounded angular. In this latter specimen, traces of a fine transverse annulation are preserved, which is directly transverse, indicating that no hyponomic sinus occurs at the peristome. In lateral view, the antisiphuncular margin is convex and the prosiphuncular margin concave. The conch height decreases nearly continuously toward the aperture resulting in maximum conch heights at or near the base of the body chamber. The siphuncle is nearly marginal, but in all specimens is too poorly preserved to be measured in all specimens.</p><p>Remarks</p><p>The endogastrically curved and contracted body chambers indicate that these belong to an unknown discosorid species, probably a cyrtogomphoceratid. The form of the body chamber (curved, contracted) in combination with a marginal siphuncle is unknown from any multiceratoid genus. However, because details of the siphuncle and the phragmocone remain unknown a firm determination and erection of a new taxon is not possible with the available material.</p></div>	https://treatment.plazi.org/id/93268783960D705AFDCEF975FCA6FC34	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783960A705BFDCDFC40FC1FFB99.text	93268783960A705BFDCDFC40FC1FFB99.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	undefined-B Flower 1950	<div><p>Discosorida fam., gen. et sp. indet. B</p><p>Fig. 46A–B</p><p>Material examined</p><p>ESTONIA • 1 spec.; Hiiumaa Island, Paluküla quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-1100 .</p><p>Description</p><p>The specimen is a fragment of a slightly endogastrically curved body chamber and two chambers of the phragmocone. The outer shell is not preserved. At the base of the body chamber, the conch height is 60 mm. The reconstructed width is 48 mm (CHI = 1.25). The conch cross section is elliptically shaped with narrow dorsal and ventral margins. In lateral view, the prosiphuncular side is concave and the antisiphuncular side convex, resulting in a slightly curved shape and a decreasing conch height. At the adoral-most parts, ca 20–30 mm from the aperture, the margins are slightly more curved, resulting in a slightly ventrally shifted apertural opening. At the aperture, the height is 52 mm. At its base a ca 7 mm wide band with oncomyarian, buttressed muscle scars is present. A hyponomic sinus is preserved on the prosiphuncular side, it is ca 10 mm deep. The body chamber is 53 mm long (RBL = 0.88).</p><p>The sutures are straight and slightly deflected adorally at the antisiphuncular side, with shallow saddles at the antisiphuncular side. The two adoral-most sutures are crowded (ca 5 mm apart), the second chamber has a length of ca 8 mm at a conch height of 60 mm (RCL = 0.13). On the adoral-most septum the septal foramen is 9 mm wide and traces of the siphuncular segments indicate a maximum expansion of the siphuncular segments to at least 15 mm (RSH = 0.15, RSS = 1.7, SCR = 1.9).</p><p>Remarks</p><p>The endogastric condition and the widely expanded siphuncle with weak or absent bullettes indicate that this specimen probably represents an unknown cyrtogomphoceratid species. The specimen differs from species of Strandoceras in having a short, contracted mature body chamber. The size of the specimen and the position and size of the siphuncle suggest that this specimen could be related to Westonoceras estonicum Balashov, 1959, another likely cyrtogomphoceratid species (not related to Westonoceras), which is known only from a single fragmentarily preserved phragmocone from late Katian strata of Tapa, Estonia. More material is needed to test this hypothesis.</p></div>	https://treatment.plazi.org/id/93268783960A705BFDCDFC40FC1FFB99	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783960B705BFDCDFB1BFDB4F851.text	93268783960B705BFDCDFB1BFDB4F851.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	undefined-C Flower 1950	<div><p>Discosorida fam., gen. et sp. indet. C</p><p>Fig. 46C–D</p><p>Material examined</p><p>ESTONIA • 1 spec.; Hiiumaa Island; Kõrgessaare quarry, Vormsi Regional Stage; TUG 1745-284 .</p><p>Description</p><p>The specimen is a mold of a complete mature body chamber. The outer shell is not preserved. The base of the body chamber has a height and width of 40 mm and 28 mm, respectively (CHI = 1.43). The body chamber is 28 mm long (RBL = 0.7). In lateral view, the antisiphuncular margin is convex and the prosiphuncular margin straight or only slightly convex near the aperture. The peristome is simple and straight, a faint hyponomic sinus is present on the prosiphuncular side. The adoralmost ca 5 mm of the body chamber are contracted. At the base, a ca 5 mm a wide band of oncomyarian, buttressed muscle scars is present. The suture is straight and directly transverse. The septal foramen is 5 mm wide and imprints on the septal mode suggest an expanded siphuncular segment with a width of at least 10 mm (RSH = 0.13, RSS = 2).</p><p>Remarks</p><p>This specimen (probably a cyrtogomphoceratid) is very similar in shape to GIT 426-1100 ( Discosorida fam., gen. et sp. indet. B) but it is smaller (height at base of body chamber: 40 mm, against 60 mm in the latter). More, and better persevered material is needed to evaluate the features of the siphuncle to assign this specimen to a (new) species.</p></div>	https://treatment.plazi.org/id/93268783960B705BFDCDFB1BFDB4F851	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396087059FDCDFEB1FCBCFE83.text	9326878396087059FDCDFEB1FCBCFE83.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	undefined-D Flower 1950	<div><p>Discosorida fam., gen. et sp. indet. D</p><p>Fig. 46E–F</p><p>Material examined</p><p>ESTONIA • 1 spec.; Sutlema old quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 1827- 162 .</p><p>Description</p><p>The specimen is a 50 mm long, fragment of a mature body chamber; it is slightly endogastrically curved with a circular conch cross section.At its base, the conch diameter is 40 mm. The suture, as reconstructed from the base of the body chamber, is straight and transverse with a distinct narrow saddle at the position of the siphuncle. The septal foramen is almost marginal with a width of 5 mm (RSH = 0.125). No traces of the outer shell are preserved.</p><p>Remarks</p><p>This relatively incomplete fragment of a mature body chamber (likely from a cyrtogomphoceratid) is documented herein, because it cannot be assigned to any of the known genera or species known from Estonia or from the literature. It differs from species of Kiaeroceras in being more strongly curved and in lacking the characteristic narrowly rounded prosiphuncular margin. It differs from species of Strandoceras in having a circular conch cross section.</p></div>	https://treatment.plazi.org/id/9326878396087059FDCDFEB1FCBCFE83	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
93268783960970A6FDA0FE4AFAFCFBA6.text	93268783960970A6FDA0FE4AFAFCFBA6.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Discoceras Barrande 1867	<div><p>Genus Discoceras Barrande, 1867</p><p>Type species</p><p>Clymenia antiquissima Eichwald, 1842, Kärdla, Hiiumaa Island, Estonia; Vormsi–Pirgu regional stages (“Lyckholm Stufe” of Teichert 1930), late Katian; by secondary designation (Schröder 1891).</p><p>Diagnosis</p><p>Tarphycerid with slightly to moderately depressed evolute shell with variously spaced frills; caecum subcentral, shifted toward ventral side, the siphuncle shifts in second and third chambers toward dorsal side, its final dorsal or subdorsal position is attained in third septum. (From Manda &amp; Turek 2018: 414.)</p><p>Remarks</p><p>The genus Discoceras was originally erected to encompass species with a subquadratic cross section and a dorsal siphuncle, which are either strongly annulated, such as in the type species or smooth such as in Lituites angulatus Saemann, 1853 (Barrande 1867). Subsequently, Discoceras has been restricted to the annulated D. antiquissimum, and smooth or slightly ribbed forms have been assigned to Schroederoceras Hyatt, 1894 .</p><p>The high ontogenetic and intraspecific variability in ornamentation and whorl cross section led Strand (1934) and Sweet (1958) to the conclusion that it is not possible to distinguish between a smooth or slightly ribbed Schroederoceras and a strongly ribbed Discoceras . Following Strand (1934: 32–33), Discoceras comprises closely coiled forms, with subquadratic to trapezoidal conch cross sections and with a sculpture “formed by imbricate lamellae which overlap in apical direction (…) and ribs, which are either strongly elevated or weaker and more closed set.” This concept of Discoceras was adopted in the Treatise (Furnish &amp; Glenister 1964) and is followed herein. It was not accepted by, e.g., Balashov (1953b), Stumbur (1962), and Dzik (1984).</p><p>Furthermore, to tackle the high intrageneric and intraspecific variability of Discoceras, Stumbur (1962) erected two new genera ( Rectanguloceras Stumbur 1962; and Sweetoceras Stumbur, 1962), rejected Sweet’s (1958) synonymisation of Discoceras and Schroederoceras, and developed a phylogenetic hypothesis based on these genera (or vice versa). However, Stumbur’s (1962) genus diagnoses do not permit effective differentiation between these two novel genera and between Discoceras and Schroederoceras, respectively. His diagnoses of the two genera are so vague, that they are inapplicable in practice.</p><p>In several specimens assigned to D. roemeri, and D. saemanni the ornamentation is preserved: The external shell is ornamented with finely crenulated, imbricate lamellae, costae or frills (see, e.g., Strand 1934: 37, 44). Additionally, a faint lateral band is visible in a specimen assigned to D. roemeri by Kröger (2013: fig. 31a, see below). Several external casts and fragments of the outer shell of species of Discoceras are preserved in the Estonian collections, which also show a longitudinal banding, which in a glance resembles a preserved color stripe. Closer examination, however, reveals that this band results from different strengths of the imbricate lamellae: at approximately mid-flank a narrow band is present with exceptionally prominent costae. Ventrally, the frills are more distinct and long: overlapping more strong than dorsal of the band.</p><p>Without doubt, the peculiar ornamentation, with a lateral band of elevated costae is a character of taxonomic value. However, it is preserved only under exceptional circumstance and, therefore, probably has never been explicitly described or included within the diagnoses of species of Discoceras, it occurs in specimens assigned to D. saemanni and D. roemeri . The feature probably is related to the “lateral furrow” described in two Silurian species of Discoceras by Manda &amp; Turek (2018).</p><p>Strand (1934) distinguished two pairs of species of Discoceras in the latest Katian strata of Norway based on the shape of the whorl cross section ( D. angulatum – D. hyatti; D. roemeri – D. saemanni). Each pair supposedly contains a species with a relatively narrow venter ( D. angulatum, D. roemeri) and a species with a broadly trapezoidal cross section and a broad venter ( D. hyatti, D. saemanni). The two pairs, in turn were distinguished by their expansion rate and relative whorl cross section width. However, the new data available from the Estonian material show that the high variability of the shape of the whorl cross section during ontogeny, within and between individual specimens does not permit distinctions between D. saemanni and D. hyatti, respectively (see below). Herein, D. hyatti is interpreted as a junior synonym of D. saemanni, leaving three late Katian species to be distinguished: one with a whorl cross section with broadly trapezoidal venter ( D. saemanni) and two with a relatively narrow venters ( D. angulatum, D. roemeri). Discoceras angulatum remains restricted to its genotype until revision. Hence, it is possible that these species represent sexual dimorphs because in many specimens, the relatively broad venter only occurs during late growth stages. A similar distinction between a species of Discoceras with a narrow venter and a species with a wide venter can be seen in D. amtjaernense Kröger &amp; Aubrechtová, 2019 and D. nilssoni Kröger &amp; Aubrechtová, 2019 from the early Katian Kullsberg Limestone, Sweden.</p></div>	https://treatment.plazi.org/id/93268783960970A6FDA0FE4AFAFCFBA6	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396F670A5FDE1FBD2FB98FC01.text	9326878396F670A5FDE1FBD2FB98FC01.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Discoceras antiquissimum (Eichwald 1842)	<div><p>Discoceras antiquissimum (Eichwald, 1842)</p><p>Fig. 47C–D, 48A, 49A, 50A</p><p>Clymenia antiquissima Eichwald, 1840: 15 (nomen nudum).</p><p>Clymenia antiquissima Eichwald, 1842: 33, pl. 3 figs 16–17.</p><p>Lituites trapezoidalis Lossen, 1860: 25, pl. 1 fig. 2.</p><p>Lituites (Trocholites) antiquissimus – Schmidt 1861: 62, pl. 6 fig. 2a–g.</p><p>Lituites antiquissimus – Roemer 1861: 62, pl. 6 fig. 2f–g (non pl. 6 fig. 2a–e = Discoceras roemeri Strand, 1934, see below); 1885: 68, pl. 4 fig. 12. ― Karsten 1869: 53, pl. 19 fig. 7a–c.</p><p>Discoceras antiquissimum – Foerste 1925: 17, 58, pl. 18 fig. 1. ― Strand 1934: 32, pl. 2 figs 4, 11, pl. 4 figs 2–3, pl. 13 fig. 9. ― Thorslund 1936: pl. 2 fig. 11. ― Balashov 1953b: 265, pl. 12 fig. 1a–b. ― Sweet 1958: 99, text-fig. 13q. ― Stumbur 1959: fig. d. ― Neben &amp; Krueger 1973: pl. 77 figs 24–25. ― Dzik 1984: 42, text-figs 9c–d, 12.39, pl. 7 fig. 1.</p><p>Discoceras antiquissima ― Hucke &amp; Voigt 1967: 58, pl. 15 fig. 1.</p><p>Diagnosis</p><p>Discoceras with adult conch diameters more than 130 mm, WER of ca 1.9, decreasing with increasing conch size; whorl cross section slightly depressed with WWI 1.2–1.5 becoming less depressed in maturity, broadly reniform in juvenile stages, rounded trapezoidal with venter wider than dorsum in later groth stages; free mature body chamber with constriction near aperture; ornamented with prominent ribs, distance between ribs is one to two times the distance between two septa; siphuncle close to dorsal conch margin, ca 0.15–0.17 of whorl height, septal necks orthochoanitic. (Adopted from Strand 1934.)</p><p>Material examined</p><p>ESTONIA • 1 spec.; sine loco; Pirgu Regional Stage; GIT 878-152 • 5 specs; Haapsalu holm; Adila Formation, Pirgu Regional Stage; GIT 225-1005, GIT 225-973, GIT 225-974, GIT 426-138, GIT 426- 375 • 3 specs; same data as for preceding; TUG 107-43, TUG 46-150, TUG 47-882 152 • 1 spec.; Hiiumaa Island, east shore between Heltermaa and Vahtrepa; Pirgu Regional Stage; TUG 66-288 • 6 specs; Vormsi Island, Hosholm shore; Adila Formation, Pirgu Regional Stage; GIT 840-246, GIT 840- 247, GIT 840-257, GIT 840-64, GIT 840-90, GIT 840-91 • 2 specs; same data as for preceding; TUG 1743-59, TUG 39-814 • 10 specs; Vormsi Island, Hosholm shore (tower locality); Adila Formation, Pirgu Regional Stage; GIT 840-255, GIT 878-140, GIT 878-141, GIT 878-208 to GIT 878-212, GIT 878-214, GIT 878-221 • 1 spec.; Inju-Meriküla quarry; Ärina Formation, Porkuni Regional Stage; GIT 426-384 • 1 spec.; Kersleti quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 939-67 • 1 spec.; Kohila; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-382 • 1 spec.; Küti, near ViruJaagupi; Kõrgessaare Formation, Vormsi Regional Stage; TUG 1745-322 • 1 spec.; Lohu (Pontiaki) springs; Adila Formation, Pirgu Regional Stage; GIT 878-137 • 1 spec.; Mahtra; Pirgu Regional Stage; GIT 426-1080 • 1 spec.; Piirsalu quarry; Moe Formation, Pirgu Regional Stage; TAM G1:170 • 1 spec.; Paluküla quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 225-1017 • 1 spec.; Piirsalu quarry; Moe Formation, Pirgu Regional Stage; GIT 426-381 • 1 spec.; same data as for preceding; TUG 46-153 • 1 spec.; Pirgu river outcrops; Adila Formation, Pirgu Regional Stage; GIT 426-383 • 1 spec,; same data as for preceding; TUG 1745-298 170 • 1 spec.; Rabivere quarry; Moe Formation, Pirgu Regional Stage; TUG 56-113 • 2 specs; Uuemõisa; Adila Formation, Pirgu Regional Stage; TAM G432:504, TAM G432:505 113 • 1 spec.; Vohilaid Island, Vohilaid outcrop 2 (2 and 3 after B. Stein); Adila Formation, Pirgu Regional Stage; GIT 878-145 • 1 spec.; same data as for preceding; TUG 66-287 • 15 specs; Vohilaid Island, Vohilaid shore (E); Adila Formation, Pirgu Regional Stage; GIT 878-147, GIT 878-148, GIT 878-197, GIT 878-199 to GIT 878-201, GIT 878-204 to GIT 878-206, GIT 878-207, GIT 878-225, GIT 878-313 to GIT 878-316 .</p><p>Type locality and horizon</p><p>Kärdla, Hiiumaa Island, Estonia; Vormsi–Pirgu regional stages (“Lyckholm Stufe” of Teichert 1930).</p><p>Description</p><p>The species has been described in detail by Strand (1934). Additional measurements, described herein, contribute to an understanding of the variability of WER and WWI (Figs 48A, 49A; supplementary data 5). The relative whorl width (WWI) decreases with conch size from ca 1.5 at whorl heights of ca 10 mm to 1.0– 1.2 in nearly adult specimens (whorl heights 30–35 mm).</p><p>The whorl expansion rate (WER) is 1.5–2.0 in nearly adult specimen, but it is considerably higher during early growth stages (maximum 3.6 in specimen GIT 426-138 at a conch diameter of 19 mm).</p><p>The largest specimen in the collections is specimen TAM G1:170 (described also in Strand 1934), a complete, mature specimen from Piirsalu, Estonia, Pirgu Regional Stage, with a diameter of 145 mm, a whorl height of 31 mm and a conch width of 31 mm. Whorl heights of 33 mm, and 31 mm, and respective widths of 36 mm and 31 mm, are known from specimen GIT 225-1005, TUG 46-153 from Pirgu Regional Stage.</p><p>Remarks</p><p>This species is unique to Discoceras because of its prominent juvenile to adult annulation. However, the strength of annulation varies between specimens, it appears to be absent in earliest growth stages (Fig. 50A), as well as during latest growth stages (Fig. 47D). The possibility exists that some variants with stronger or weaker annulation represent different species. However, the available material does not permit differentiation between species with different annulation patterns.</p></div>	https://treatment.plazi.org/id/9326878396F670A5FDE1FBD2FB98FC01	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396F570A1FD9BFBB2FE91FE69.text	9326878396F570A1FD9BFBB2FE91FE69.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Discoceras paopense Kröger 2025	<div><p>Discoceras paopense sp. nov.</p><p>urn:lsid:zoobank.org:act: 22516E44-23DC-42BD-9D93-444068FBC3F0</p><p>Figs 47A–B, 48A, 49A, 51C</p><p>Diagnosis</p><p>Discoceras with large adult conch diameters of more than 120 mm, adult WER ca 1.7–2, decreasing with increasing conch size; whorl cross section slightly compressed with WWI 0.8–0.9 in mature stages, with flattened venter not wider than dorsum; free whorl in mature growth stages; ornamented with irregularly spaced costae and distinct shallow ribs, ca three to four costae occur between two ribs, the ribs and the costae run obliquely across the umbilical margin and form a deep U-shaped hyponomic sinus.</p><p>Etymology</p><p>Refers to the type locality.</p><p>Type material</p><p>Holotype</p><p>ESTONIA • Paope quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 2-719.</p><p>Paratypes</p><p>ESTONIA • 3 specs; same data as for holotype; GIT 426-114, GIT 426-35, GIT 426-373 • 1 spec.; sine loco; Kõrgessaare Formation, Vormsi Regional Stage; TUG 2-730 • 1 spec.; Vormsi Island, Saxby shore; Kõrgessaare Formation Vormsi Regional Stage; GIT 426-160 .</p><p>Description</p><p>The holotype, TUG 2-719, consists of ⅔ of a mold of a whorl with a conch diameter of 88 mm of which only the apical 33 mm of the phragmocone are preserved in 3D (Fig. 47B). The other parts are strongly flattened, without inner septa and siphuncle preserved. The whorl height at the maximum diameter is 28 mm. At a whorl width of 19 mm, the corresponding whorl height is 19 mm. There, the conch cross section is rounded, subquadratic. At a whorl width of 19 mm, the septal distance is 2–3 mm. The conch surface is ornamented with shallow annulations in a distance of 3–4 mm at the venter combined with distinct striae, which run parallel to the annuli with ca 4–5 striae per cycle of annulations. The annuli and striae form a deep and broadly rounded hyponomic sinus (in the inner whorls of the specimen ca 5 mm deep) and exhibit an apically deflected, curved path over the flanks.</p><p>The largest and most complete specimen is TU 2-730 (Fig. 47A). This specimen is a mold of a nearly mature individual with a maximum diameter of 119 mm. The preserved part of the body chamber is 105 mm long and spans nearly 45°, it is detached from the rest of the conch at a diameter of ca 114 mm. The whorl cross section of the adoralmost part of the body chamber has a width of ca 28 mm and a height of 32 mm, at the base of the body chamber the width is 25 mm and the height 28 mm, its umbilical flanks are rounded with the greatest width near the dorsum, the venter is flattened with the flattened part narrower than the umbilical margin. The cross section in a juvenile part of the conch is rounded with a width and height of 14 mm.</p><p>The septal distance at the base of the body chamber is 4–5 mm. The sutures form shallow, wide lobes on the umbilical flanks and on the venter and a pointed saddle at the ventrolateral shoulders.</p><p>The ornamentation consists of shallow, irregularly spaced, but distinct annuli (at the base of the body chamber ca three occur at a length of 10 mm). Between the annuli, ca two to four costae are present. The ornamentation runs obliquely across the umbilical margins of the whorl and forms a deep broad hyponomic sinus.</p><p>Specimen GIT 426-114 is a 75 mm long fragment of a mold of a body chamber with a rounded subquadratic cross section with a whorl width of 30 mm and a whorl height of 26 mm. The specimen is ornamented with annuli (ca 3 in a distance of 10 mm) which run obliquely, curved at the flanks adapically and form a deep and U-shaped hyponomic sinus (&gt; 10 mm deep).</p><p>Specimen GIT 426-351 is a well-preserved mold of a phragmocone with a rounded subquadratic to trapezoidal cross section with greatest whorl width of 23 mm near the flattened venter and with a whorl height of 20 mm. The ornamentation is identical to that of specimen GIT 426-114. The siphuncular foramen is located at the dorsal margin of the septum and has a diameter of 4.5 mm (RSH = 0.23).</p><p>Specimen GIT 426-373 is a fragment of a phragmocone with a rounded subquadratical conch cross section with whorl width 13 mm and corresponding whorl height of 11 mm. The septal distance is 2.5 mm and the siphuncular foramen is located at the dorsal margin with a diameter of 2 mm (RSH = 0.18). The specimen is ornamented with distinct annuli, which run obliquely over the flanks and form a deep U-shaped hyponomic sinus, ca 4 annuli occur per 10 mm.</p><p>Remarks</p><p>The most complete specimen (TUG 2-230) of this new species cannot serve as a holotype, because it is from an unknown locality (although its stratigraphy, Vormsi Regional Stage, is stated on the label, which is coherent with the distinct Kõrgessaare Formation lithology of the specimen).</p><p>Comparison</p><p>The new species differs from D. antiquissimum in ornamentation. In contrast to the latter, the path of the ornament follows a broad curve obliquely across the umbilical margin of the whorl, forming a deep U-shaped hyponomic sinus. It consists of a succession of alternating strong annuli and weaker costae (ca two to three) in between two ribs. The ornamentation is more similar to that of D. boreale Sweet, 1958, and D. arcuatum (Lossen, 1860) . Discoceras paopense sp. nov. differs from both these species, in having a whorl cross section of the aspect of D. roemeri with a flattened venter. The relatively low WWI of D. paopense sp. nov. is similar to that of D. rarospira (Eichwald, 1860), but the latter species differs in having a more rounded whorl cross section and a siphuncle that is further from the dorsal conch margin.</p><p>Probably, the specimen assigned to D. antiquissimum, and figured in Dzik (1984: pl. 7.1.) from erratic boulders of Poland (collection of Roemer 1861) belongs to D. paopense sp. nov. because it has a similar ornamentation. This specimen, however, differs in having a (taphonomically?) depressed whorl cross section.</p></div>	https://treatment.plazi.org/id/9326878396F570A1FD9BFBB2FE91FE69	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396F170AAFDA6FE0CFE42FEA2.text	9326878396F170AAFDA6FE0CFE42FEA2.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Discoceras roemeri Strand 1934	<div><p>Discoceras roemeri Strand, 1934</p><p>Figs 48B, 49B, 51D, E, 52E, 53</p><p>Discoceras roemeri Strand, 1934: 38, 42–43, pl. 2 figs 6a–b, 7, pl. 5 figs 1–2.</p><p>Schroederoceras balaschovi Stumbur, 1956: 181, pl. 1 figs 5–6.</p><p>Lituites antiquissimus – Roemer 1861: 62, pl. 6 fig. 2a–e (non pl. 6 fig. 2f–g = Discoceras antiquissimum (Eichwald, 1840)) . Schroederoceras angulatum – Teichert 1930: 276. ― Balashov 1953b: 263, pl. 13 figs 1a–b, 2a–b. Discoceras angulatum – Mutvei 1957: text-fig. 12, pl. 8.</p><p>Discoceras roemeri – Sweet 1958: 99, 102, text-fig. 13p. ― Dzik 1984: 41, 44, text-figs 10, 12.43, pl. 6 figs 5–6.</p><p>Schroederoceras roemeri – Stumbur 1962: 136, text-fig. 2.4.</p><p>Rectanguloceras balaschovi – Stumbur 1962: 142, text-fig. 2.9.</p><p>Rectanguloceras (Discoceras) cf. roemeri – Neben &amp; Krueger 1973: pl. 65 figs 1–2.</p><p>Diagnosis</p><p>Discoceras with large adult conch diameters of&gt; 140 mm, WER ca 1.9–2.5, decreasing with increasing conch size; whorl cross section slightly depressed with WWI ca 1.1–1.3, rounded, subquadratic with venter not wider than dorsum; body chamber nearly 180° long, free in mature growth stages and becoming markedly higher during mature stages; ornamented with imbricated lamellae, irregularly spaced costae and shallow ribs. (From Kröger 2013.)</p><p>Material examined</p><p>ESTONIA • 1 spec.; Aulepa quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 895-149 • 1 spec.; sine loco; Vormsi – Pirgu regional stages; GIT 426-379 • 1 spec.; same data as for preceding; TAM G432:597 • 1 spec.; Förby shore; Pirgu Regional Stage; TUG 1745-175 • 1 spec.; Haapsalu holm; Adila Formation, Pirgu Regional Stage; TUG 939-74 • 1 spec.; Vormsi Island, Hosholm shore; Adila Formation, Pirgu Regional Stage; GIT 840-250 • 1 spec.; same data as for preceding; TUG 119-624 • 1 spec.; Vormsi Island, Hosholm shore (tower locality); Adila Formation, Pirgu Regional Stage; GIT 878-230 • 8 specs; Jootma ditch; Moe Formation, Pirgu Regional Stage; GIT 426-368, GIT 426-369, GIT 426-385, GIT 426-403 to GIT 426-405, GIT 426-441, GIT 426-442 • 1 spec.; Kernu quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-380 • 1 spec.; Kohila; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-424 • 1 spec.; Kolu quarry; Pirgu Regional Stage; GIT 426-364 • 4 specs; Kõrgessaare quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-396, GIT 426- 400 to GIT 426-402 • 1 spec.; same data as for preceding; TUG 895-68 • 1 spec.; Küti, near ViruJaagupi; Kõrgessaare Formation, Vormsi Regional Stage; TUG 1745-324 • 1 spec.; Lehtse; Kõrgessaare Formation, Vormsi Regional Stage; TAM G432:593 • 1 spec.; same data as for preceding; TUG 42-368 • 1 spec.; Moe, Pirgu Regional Stage; GIT 426-366 • 1 spec.; Moe trench; Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-106 • 2 specs; Niibi hillock; Moe Formation, Pirgu Regional Stage; TUG 39-711, TUG 42-290 • 1 spec.; Odulemma old quarry; Nabala Regional Stage; GIT 426-365 • 5 specs; Paluküla quarry; Kõrgessaare Formation, Vormsi Regional; Stage; GIT 426-419, GIT 426-420, GIT 426-434, GIT 426-435, GIT 878-135 • 1 spec.; same data as for preceding; TUG 2-732 • 11 specs; Paope quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-1076 to 426-1078, GIT 426- 349, GIT 426-350, GIT 426-353, GIT 426-406, GIT 426-407, GIT 426-410, GIT 426-415, GIT 426-417 • 1 spec.; same data as for preceding; TUG 1745-206 • 1 spec.; Röa-Jakobi quarry; Ärina Formation, Porkuni Regional Stage; GIT 426-425 • 1 spec.; Saaremõisa (Lyckholm); Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-122 • 1 spec.; same data as for preceding; TAM G432:680 • 1 spec.; same data as for preceding; TUG 1745-172 • 1 spec.; Saksi manor; Pirgu Regional Stage; TUG 2-284 • 1 spec.; Salu; Pirgu Regional Stage; GIT 426-362 • 1 spec.; same data as for preceding; TUG 939- 77 • 3 specs; Vormsi Island, Saxby shore; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426- 113, GIT 426-343, GIT 426-348 • 1 spec.; same data as for preceding; TUG 44-41 • 8 specs; Vormsi Island, Saxby shore (N); Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-1068, GIT 426-1069, GIT 878-24, GIT 878-29, GIT 878-38, GIT 878-48, GIT 878-52, GIT 878-73 • 1 spec.; Sutlema old quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 1827-164 • 1 spec.; Sutlepa quarry; Adila Formation, Pirgu Regional Stage; TUG 2-651 • 1 spec.; Tapa; Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-98 • 2 specs; Vohilaid Island, Vohilaid shore (E); Adila Formation, Pirgu Regional Stage; GIT 878-202, 2 GIT 878-203 • 1 spec.; same data as for preceding; TUG 1723-27 .</p><p>Type locality and horizon</p><p>Herøya, near Porsgrunn, Norway; Herøya Formation (“Gastropod limestone”), latest Katian Stage (Strand 1934).</p><p>Description</p><p>Specimen GIT 878-230 is an exceptionally well-preserved, complete mature specimen (Figs 51E, 52E). This specimen has a conch diameter of 123 mm, the base of the body chamber is at a conch diameter of 105 mm. The body chamber is 107 mm long and extends around ca ¼ of a volution. The body chamber diverges from the rest of the conch at ca 112 mm. The sutures form wide lobes over the umbilical margin and are nearly straight at the venter. They are ventrally 10 mm apart where the corresponding conch diameter is 105 mm. At the aperture, the whorl is slightly constricted and forms wide U-shaped hyponomic sinus. At the aperture, the whorl cross section is subquadratic with a rounded venter, the whorl cross section has a distinctively flattened venter at the base of the body chamber. There, the whorl width, and height are 33 mm, and the umbilical margins are slightly rounded with their greatest width near the mid-flank. At a conch diameter of 69 mm, the whorl cross section has a width of 29 mm and a height of 27 mm, and the venter is distinctively flattened. There, the umbilical margins are rounded with greatest width at mid-flanks. The path of the ornament follows a broad U-shaped hyponomic sinus on the venter (Fig. 52E). The costae are irregularly spaced: at a conch diameter of 80 mm, ca six to seven occur at a length of 10 mm at the venter. On the first three whorls at ca mid-flank position, a 2–3 mm wide band is present in which the lamellae are slightly more pronounced and thicker. Ventrally of that band, the lamellae generally appear to be slightly longer, creating a stronger relief. On the external cast of this specimen, parts of the shell are attached at the position of the longitudinal band and ventrally, giving the false impression of a longitudinal color banding (see also Fig. 52C).</p><p>Four specimens are preserved with the mature divergence of the body chamber; in one of them the divergence occurs at a conch diameter 93 mm (TUG 1745-175); in the others it occurs at diameters 118 mm (GIT 878-230), 124 mm (TUG 1723-27) (Fig. 51D), and 125 mm (TUG 2-651). The only complete adult specimens in the collection are GIT 878-230, and TUG 1723-27 with adult diameters of 124 mm and 128 mm, respectively.</p><p>Remarks</p><p>The specimens described by Balashov (1953b) under Schroederoceras roemeri, represent a different species. Based on similarities in ornamentation and siphuncular position, they are probably related to D. boreale Sweet, 1958 .</p><p>The finely transversely lamellate or costate conch surface (Fig. 52) is not preserved in most specimens because it is often firmly attached to the external sediment. During natural weathering or artificial preparation, the shell splits from the smooth, inner cast of the specimen and the surface of its external side remains invisible. In few, exceptionally preserved specimens, a peculiar ornamentation is visible: in superficial view it is longitudinal banded, giving the impression of a color band at approximately mid-flank position (compare, e.g., Kröger &amp; Aubrechtová 2019: fig. 5). The apparent banding, however, is produced by subtle differences in ornamentation between the dorsal part of the flank and the ventral part of the flank and the venter: the frills or crenulate lamellae are deeper and more pronounced at the ventral section of the flank.</p><p>Comparison</p><p>The holotype of D. roemeri is a large, mature specimen (conch diameter ca 140 mm, Strand 1934: 45). In comparison, the holotype of D. angulatum, which also is a complete mature specimen and the only type specimen of this species (see Strand 1934), is small (diameter ca 90 mm, Strand 1934: 37). The shape of the whorl cross section of D. roemeri is described as “rounded quadrangular” (Strand 1934: 43), whilst that of D. angulatum was described as “subquadrangular […] with the venter narrower than the dorsum” (Strand 1934: 37). Additionally, the length of the mature body chamber differs between the types of the two species: in D. roemeri it is ca ½ of a volution, whilst it is only ¼ of a volution in D. angulatum . The types of D. angulatum and D. roemeri differ also in WWI, with D. angulatum having a smaller WWI at a comparable conch size (Fig. 49B; supplementary data 5). Despite these differences in the types, it is impossible to distinguish between the two species in the Estonian material.</p><p>The WWIs of the Estonian specimens assigned to D. roemeri, herein, are generally lower than of the Norwegian types of this species at comparable growth stages, and are more similar to that of the type of D. angulatum (Fig. 49B). However, several of the measured specimens in the Estonian collections are also larger than 90 mm in conch diameter, and therefore could only be placed within D. angulatum after emending the diagnosis of this species and accepting larger adult conch diameters. To distinguish different species based on WWI is not possible, as no sharp boundaries exist between the two groups.</p><p>Distinction between the two species based on the whorl cross sections is also not possible in the Estonian material. Many interspecific and ontogenetic variations of D. angulatum -like and D. roemeri -like whorl cross section shapes occur in the Estonian material, with a flattened, slightly rounded venter, and subquadratic to broadly reniform shapes (Fig. 53; also compare Strand 1934: pl. 2 figs 3, 5–7). This is also the case in a specimen figured by Kröger (2013: fig. 32a) assigned to D. roemeri, where the premature whorl cross section is almost identical to that of the adult D. angulatum . It is therefore impossible to distinguish between D. angulatum and D. roemeri in premature specimens with conch diameters &lt;90 mm.</p><p>Furthermore, the available material does not permit distinctions between two or more size classes of maturity. Among the seven type specimens of D. roemeri described by Strand (1934), four have a conch diameter of more than 130 mm. The Estonian material contains four mature specimens belonging to the D. angulatum – D. roemeri group, three of them have mature conch diameters of more than 120 mm (see above). An additional specimen with a mature conch diameter of ca 100 mm is known from Balashov 1953b: pl. 13 fig. 1a–b, described under Schroederoceras angulatum . With these data it is not possible to distinguish between clearly constrained size-groups of D. roemeri and D. angulatum .</p><p>Too little is known about the intraspecific and ontogenetic variability of the length of the body chamber. Significant differences exist between specimens described, herein (compare Fig. 51D–E). However, the low number of specimens with complete body chambers available does not permit the detection of sets of features covarying with the body chamber length. Future work (that includes the Norwegian material) may show whether D. roemeri is a subjective junior synonym of D. angulatum or if both species represent distinct groups. Therefore, for practicality, herein, we assign specimens with a D. angulatum – D. roemeri aspect to the latter and reserve D. angulatum to specimens with small adult size and an adult conch cross section identical to the type of this species.</p><p>Discoceras roemeri differs from D. saemanni, which also has a distinctively flattened venter, in having a whorl cross section with greatest width between the venter and the dorsum, but not strictly at the venter. Throughout the entire length of the conch, the umbilical margins are generally more rounded in D. roemeri compared to D. saemanni . The average WER of mature D. roemeri is ca 1.8–1.9; slightly lower than that of mature D. saemanni (WER ca 2.0) (compare Fig. 48B–C for ontogenetic trends; supplementary data 5).</p></div>	https://treatment.plazi.org/id/9326878396F170AAFDA6FE0CFE42FEA2	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396FA70A9FDB7FED5FAFCFD5A.text	9326878396FA70A9FDB7FED5FAFCFD5A.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Discoceras saemanni (Hyatt 1894)	<div><p>Discoceras saemanni (Hyatt, 1894)</p><p>Figs 48C, 49C, 50B, 51A, 53</p><p>Lituites angulatus Saemann, 1853: 166, pl. 21 fig. 1c–d, (not 1a–b).</p><p>Trocholites undosus Foord, 1891: 45 .</p><p>Schroederoceras saemanni Hyatt, 1894: 462 .</p><p>Discoceras hyatti Strand, 1934: 38–39, pl. 2 fig. 2, pl. 5 fig. 3a–b.</p><p>Discoceras sp. – Foerste 1929: 176, pl. 20 fig. 2a.</p><p>Discoceras saemanni – Strand 1934: 40–42, pl. 2 fig. 1a–b, pl. 4 fig. 1. ― Sweet 1958: 102, fig. 13n.</p><p>Discoceras hyatti – Sweet 1958: 102, fig. 13g. ― Dzik 1984: 44, text-fig. 12.43.</p><p>Schroederoceras hyatti – Stumbur 1959: 26, fig. 1v.</p><p>Schroederoceras saemanni – Stumbur 1962: 137.</p><p>Emended diagnosis</p><p>Discoceras with adult conch diameters of up to ca 125 mm; mature WER of ca 2.0; mature whorl cross section with WWI ca 1.1–1.2, subtrapezoidal with flattened venter, venter considerably wider than dorsum except at adult aperture and in juvenile growth stages; WER and WWI decrease with conch size; free mature body chamber with constriction near aperture; ornamented with crenulated costae and distinct growth lines that form a U-shaped hyponomic sinus, low ribs can occur.</p><p>Material examined</p><p>ESTONIA • 1 spec.; sine loco; Vormsi Regional Stage; TAM G432:598 • 2 specs; same data as for preceding; TUG 1745-59, TUG 666-298 • 3 specs; Hosholm shore; Adila Formation, Pirgu Regional Stage; GIT 426-354 to GIT 426-356 • 1 spec.; Imastu old quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 42-366 • 1 spec.; Jootma ditch; Moe Formation, Pirgu Regional Stage; GIT 426-1137 • 1 spec.; Kersleti; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-377 • 3 specs; Kõrgessaare quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-361, GIT 426-395, GIT 426-429 368 • 1 spec.; Moe stratotype outcrop; Moe Formation, Pirgu Regional Stage; TUG 42-367 • 1 spec.; Moe trench; Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-107 • 2 specs; Niibi hillock; Moe Formation, Pirgu Regional Stage; GIT 426-357, GIT 426-358 • 3 specs; same data as for preceding; TAM G432:423, TAM G432:424, TUG 939-66 • 1 spec.; Oru manor; Kõrgessaare Formation, Vormsi Regional Stage; TUG 2-715 • 1 spec.; Paluküla quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-422 • 2 specs; same data as for preceding; TUG 47-880, TUG 66-294 • 8 specs; Paope quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-159, GIT 426-352, GIT 426-408, GIT 426- 413 to GIT 426-416, GIT 426-1074, GIT 426-1075 • 1 spec.; Rannaküla old quarry; Adila Formation, Pirgu Regional Stage; GIT 426-360 • 1 spec.; Saaremõisa (Lyckholm); Kõrgessaare Formation, Vormsi Regional Stage; TUG 72-342 • 1 spec.; Salu; Pirgu Regional Stage; GIT 426-36377 • 20 specs; Vormsi Island, Saxby shore; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-107, GIT 878-155, GIT 426-109, GIT 426-112, GIT 426-342, GIT 426-344, GIT 426-345, GIT 426-347, GIT 878-155, GIT 426-1071 to GIT 426-1073, GIT 878-17, GIT 878-22, GIT 878-56, GIT 878-64, GIT 878-66 to GIT 878-69 • 12 specs; same data as for preceding; TUG 39-710, TUG 44-40, TUG 66-290 to TUG 66-292, TUG 119-625, TUG 666-296, TUG 939-65, TUG 1666-16, TUG 1743-36, TUG 1743-5, TUG 1745-214 • 1 spec.; Sutlepa quarry; Adila Formation, Pirgu Regional Stage; GIT 426-359 • 2 specs; same data as for preceding; TAM G432:502, TAM G432:503 • 1 spec.; same data as for preceding; TUG 39-706 • 1 spec.; Tapa; Kõrgessaare Formation, Vormsi Regional Stage; TUG 1745-22 .</p><p>Type locality and horizon</p><p>Herøya, near Porsgrunn, Norway; Herøya Formation (“Gastropod limestone”), latest Katian Stage (Strand 1934).</p><p>Description</p><p>The species has been described by Strand (1934) based on Saemannʼs (1853) specimen of Lituus angulatus and three additional specimens of D. saemanni, all of them have conch diameters of more than 100 mm, the largest has a mature diameter of 125 mm. The two specimens, described by Strand (1934) under D. hyatti, are smaller, with mature conch diameters of 84 mm and 95 mm, respectively. In three specimens of the Estonian material, the mature divergence of the body chamber is preserved; it occurs at a conch diameter of 74 mm in TUG 1745-214, and at 110 mm in GIT 426-425.</p><p>GIT 426-425 is a fragment of a mature specimen with the complete adult body chamber preserved (Fig. 50B). The diameter at the base of the body chamber is ca 100 mm. The body chamber is ca 100 mm long and has a trapezoidal cross section at its base. There, it is widest at the venter with a width of 34 mm and a height of 30 mm (WWI = 1.13). The adult aperture has a subquadratic, rounded cross section and a width of 32 mm. The specimen has a subquadratic conch cross section at a diameter of 33 mm with a conch width of 15 mm and corresponding conch height of 11 mm (WWI = 1.36). At a conch diameter of 51 mm, the conch cross section is rounded subquadratic with a flat venter and a maximum width at mid-flank of 18 mm, and with a corresponding height at 17 mm (WWI = 1.06).</p><p>A change from a subquadratic whorl cross section with maximum width at mid-flank to trapezoidal whorl cross section with its maximum width at the venter occurs at conch diameters of ca 40–50 mm and corresponding conch widths of 16–17 mm (e.g., TUG 1745-59, GIT 426-345, GIT 426-354, GIT 426-425, GIT 426-1072).</p><p>The ornamentation is well-preserved in specimens GIT 426-425 and 426-391, where it forms well-developed, irregularly spaced, crenulated costae or frills which are imbricated toward the aperture, and which form a wide U-shaped hyponomic sinus. The costae are more regularly spaced in juvenile portions (first one–two volutions), with a distance of ca 1 mm at the venter; they are less distinct in later growth stages and on the mature body chamber with a distance of ca 1–1.5 mm at the venter. In specimen GIT 426-425, a distinct band is apparent at mid-flank in the first two whorls, where the frills appear to be more elevated and broken off the remainder of the shell. On the initial ca two volutions of specimen GIT 878-67, the costae are developed more strongly at distances of 3–4 mm, forming low ribs. In specimen GIT 878-67, the mold preserves the ornamentation and the septa and shows that ca three costae occur in the distance between two successive septa on the second volution. Identical features of the ornamentation are best preserved and figured, in specimens assigned herein to Discoceras sp. (Fig. 52A–C).</p><p>The features of the siphuncle and septal neck are well-preserved in specimen GIT 426-107. The siphuncle is located at the dorsal margin of the whorl throughout its preserved length (conch diameter 41–92 mm). At a conch diameter of 92 mm, the whorl height is 24 mm, and the diameter of the septal foramen is 4 mm (RSH = 0.17), and the septal distance is 4.5 mm. At a position with whorl height 19 mm, the septal foramen is 2.5 mm in diameter (RSH = 0.13); the septal distance is 4 mm. The septal neck is straight, suborthochoanitic and 1.5 mm long. The connecting ring is 0.7 mm thick, reaching its greatest thickness near the adapical part of the segment.</p><p>Remarks</p><p>The emendation herein regards the variability of the adult size (given as ca 120 mm in Strand 1934), and the WWI (given as 1.2–1.5 in Strand 1934). Because of the high ontogenetic variability of this character, the range of the mature WWI rather than its total range throughout the growth of the conch (as used by Strand 1934) is included in the diagnosis. The maximum adult size is taken from the largest of the types described by Strand (1934: 41) under this species.</p><p>Strand (1934) distinguished D. saemanni from D. hyatti based on the whorl cross section (wider in the former) and by the expansion rate (lower in the latter). However, a comparison of the WWI and WER of the types of Strand (1934) reveals that these differences are well within the variability of the Estonian sample (see Fig. 48C). The combined samples of D. saemanni and D. hyatti from Norway (i.e., the Strand 1934 types) and from Estonia differ in WWI but not in WER (see Table 2). However, the variation between specimens appears to form a continuum between the extremes. Therefore, a distinction between two species based on expansion rate and whorl shape is practically impossible with the available material.</p><p>Additionally, the ontogenetic trends between the types of D. saemanni and D. hyatti differ, their WWI decreases with conch size in the former, and it remains relatively constant in the latter (see, e.g., Strand 1934: pl. 2 figs 1–2; Fig. 49C). However, the Estonian material contains specimens with decreasing, increasing, and nearly constant WWI trends, and specimens in which WWI initially increases and later decreases. In total, these trends result in a decreasing WWI–conch size relation (Fig. 49C) and it is impossible to distinguish morphologically well-delimited groups among them.</p><p>Strand (1934) also mentioned the ornamentation as a feature that distinguishes D. saemanni from D. hyatti, but it remains unclear what exactly these differences are. In both species, he described similar distinct costae and growth lines and the occurrence of low ribs during juvenile growth stages. In the Estonian material, it was not possible to distinguish two or more groups based on differences in ornamentation. Consequently, D. hyatti is interpreted as a junior synonym of D. saemanni herein.</p><p>Comparison</p><p>Discoceras saemanni differs from D. roemeri and D. angulatum in having a whorl cross section with greatest width at the venter. In D. roemeri and D. angulatum, the greatest width occurs at a position of the umbilical shoulders but not at the venter. In D. roemeri and D. angulatum, the umbilical shoulders are generally more rounded throughout their conch lengths.</p><p>In several specimens of D. saemanni, the whorl cross section changes during ontogeny from rounded, subquadratic or depressed reniform in early growth stages to trapezoidal with greatest width at the venter during later ontogeny (Fig. 53). This change occurs at diameters of smaller than ca 50 mm, and at whorl widths smaller than 17 mm. It is therefore impossible to distinguish between D. saemanni, D. roemeri, and D. angulatum in specimens with diameters below ca 50 mm, and with whorl widths below 17 mm when the whorl cross section is not unambiguously trapezoidal. However, in several specimens assigned to Discoceras saemanni (including a specimen figured in Strand 1934: pl. 2 fig. 1a), a trapezoidal whorl cross section with its greatest width at venter appears already from the first volution onward, making such a distinction possible. As a general ontogenetic trend, a change from a more rounded toward a more flattened venter occurs in all specimens (Fig. 53). In mature specimens, however, the aperture, again, is rounded and has no flattened venter. A considerable intraspecific and ontogenetic variation occurs also in ornamentation of D. saemanni, with at least one specimen (GIT 426-1072), showing an annulation on the inner two whorls.</p><p>The embryonic shells of specimens assigned to D. hyatti and D. antiquissimum have been described by Stumbur (1959). In both species, the first whorl is tightly coiled, leaving no or only a very narrow umbilical window and comprising five ( D. hyatti) to seven ( D. antiquissimum) chambers. The diameters of the embryonal shell are 10.1 mm for D. hyatti, and 14.7 mm for D. antiquissimum (Stumbur 1959) . In both species the siphuncle starts near the venter in the first chamber, perforates the first septum slightly ventral from the whorl center and reaches a nearly dorsal position at the 3 rd to 4 th septum (Stumbur 1959).</p></div>	https://treatment.plazi.org/id/9326878396FA70A9FDB7FED5FAFCFD5A	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396F970A9FDB5FD5DFDF4F959.text	9326878396F970A9FDB5FD5DFDF4F959.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	undefinedA	<div><p>Multiceratoidea gen. et sp. indet. A</p><p>Fig. 45C–E</p><p>Material examined</p><p>ESTONIA • 1 spec.; Pirgu River outcrops; Adila Formation, Pirgu Regional Stage; TUG 1745-299 • 1 spec.; Vormsi Island, Hosholm shore (tower outcrop); Adila Formation, Pirgu Regional Stage; GIT 840-269 • 1 spec.; Vormsi Island, Saxby shore; Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-76 .</p><p>Description</p><p>GIT 840-269 (Fig. 45C) is a fragment of a phragmocone, exogastrically curved with an angle of expansion of 20° at a conch height between 37 mm and 26 mm. At its apical end, the height and width are 26 mm and 23 mm, respectively (CHI = 1.13). The septa are 6 mm apart where the conch height is 31 mm (RCL = 0.19), and the sutures form lateral lobes. The siphuncle is marginally positioned and expands into the chambers. The septal foramen is 2.5 mm wide where the conch height is 26 mm (RSH = 0.1).</p><p>GIT 840-76 (Fig. 45D–E) is an exogastrically curved fragment of a phragmocone with a conch height and width of 20 mm and 18 mm, respectively, at its apical end (CHI = 1.11) with sutures which form lateral lobes. The sutures are 5 mm apart where the conch height is 23 mm (RCL = 0.22). The conch curvature, CHI, RCL and curvature of the suture line are similar to that of GIT 840-269.</p><p>TUG 1745-299 is a fragment of a phragmocone of an apparently exogastric cyrtocone with a conch width of 24 mm. It is closely similar to the two specimens, but too poorly preserved to be measured.</p><p>Remarks</p><p>These three specimens are described in order to document the presence of a relatively large, exogastrically curved brevicone, different from the genera and species described herein, but not well enough known to determine the order, genus, or species.</p></div>	https://treatment.plazi.org/id/9326878396F970A9FDB5FD5DFDF4F959	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396F970B6FDB4F95BFAFDFD3E.text	9326878396F970B6FDB4F95BFAFDFD3E.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	undefinedB Mutvei 2013	<div><p>Multiceratoidea gen. et sp. indet. B</p><p>Fig. 39C</p><p>Material examined</p><p>ESTONIA • 1 spec.; Vormsi Island, Saxby shore; Kõrgessaare Formation, Vormsi Regional Stag; TUG 1743-37 .</p><p>Description</p><p>The specimen is a fragment of a curved adoral part of a mature body chamber. The complete length of the fragment is 63 mm. At the aperture, the conch is 50 mm high and slightly compressed, a shallow apertural sinus (hyponomic?) occurs at the side of the conch which in lateral profile forms the convex conch margin. Otherwise, the peristome was apparently straight, transverse. At its apical end, 47 mm from the aperture, the conch has a diameter of 55 mm and is circular in cross section. In lateral view, on the convex side of the conch curvature shallow, irregularly spaced ribs occur, which are ca 15 mm apart. The conch surface is ornamented with distinct growth lines.</p><p>Remarks</p><p>The available information about this species, i.e., the contracted curved body chamber, compressed conch cross section, hyponomic sinus on the convex side of the conch curvature suggest that it belongs to an unknown annulated multiceratoid. More complete material is needed for a definite determination.</p></div>	https://treatment.plazi.org/id/9326878396F970B6FDB4F95BFAFDFD3E	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
9326878396E670B6FDB4FCBAFDA3F9D0.text	9326878396E670B6FDB4FCBAFDA3F9D0.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	undefinedC Mutvei 2013	<div><p>Multiceratoidea gen. et sp. indet. C</p><p>Fig. 28K–L</p><p>Material examined</p><p>ESTONIA • 1 spec.; Vormsi Island, Hosholm shore (tower locality); Adila Formation, Pirgu Regional Stage; GIT 878-234 .</p><p>Description</p><p>The specimen is an exogastrically curved fragment of a body chamber and one chamber of the phagmocone. The outer shell is not preserved but the surface was apparently smooth or ornamented with faint transverse lirae. At the base of the body chamber, the conch height and width are 17 mm and 14 mm, respectively (CHI = 1.21). The conch cross section is oval compressed with a narrower conch margin on the prosiphuncular side. The conch has an angle of expansion of 18°. The body chamber has a preserved length of ca 15 mm. In lateral view, both conch margins are curved, convex on the prosiphuncular and concave on the antisiphuncular side. The two preserved septa are 2.2 mm apart (RCL = 0.13), and their sutures form shallow lateral lobes. The siphuncle is located near the convex margin of the conch with a septal foramen which is too poorly preserved to be measured.</p><p>Remarks</p><p>The fragmentary character of this specimen does not allow further determination. It is not clear whether this fragment represents a mature individual or a juvenile specimen. Cyrtorizoceras tenue Strand, 1934 has a similar angle of expansion (18°) and a CHI of 1.25 but is too poorly known to be compared with the specimen described herein.</p></div>	https://treatment.plazi.org/id/9326878396E670B6FDB4FCBAFDA3F9D0	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Kröger, Björn	Kröger, Björn (2025): The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia. European Journal of Taxonomy 978: 1-169, DOI: 10.5852/ejt.2025.978.2801, URL: https://europeanjournaloftaxonomy.eu/index.php/ejt/article/download/2801/12801
