Hiiumoceras hiiuense, Kröger, 2025

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, pp. 1-169 : 74-76

Hiiumoceras hiiuense gen. et sp. nov.

urn:lsid:zoobank.org:act:CBB9CFFF-F108-4D62-8667-64A3318EE96D

Figs 28A–D , 29A

Diagnosis

Same as for genus, by monotypy.

Etymology

Refers to the Hiiumaa, Estonia, the region, where this species is known from.

Type material

Holotype

ESTONIA • Hiiumaa Island, Paope quarry ; Kõrgessaare Formation , Vormsi Regional Stage; TUG 1745- 11 .

Paratype

ESTONIA • 1 spec.; Hiiumaa Island, Paluküla quarry ; Kõrgessaare Formation , Vormsi Regional Stage; GIT 426-421 .

Description

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.

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).

Comparison

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.

Figures

Fig. 28. Graciloceratidae Flower, 1950 and Oncoceratidae Hyatt, 1884 of the Vormsi–Pirgu regional stages, Estonia. A–D. Hiiumoceras hiiuense gen et sp. nov., paratype GIT 426-421, from Paluküla, Hiimuaa Island, Vormsi Regional Stage. A. Lateral view. B. View of antisiphuncular side. C. View of prosiphuncular side. D. Adapical view. E. Rizosceras teres sp. nov., holotype TUG 1745-188, from Saaremõisa (Lyckholm), Vormsi Regional Stage, view of prosiphuncular side with details of siphuncle visible. F, I–J. Beloitoceras (?) sp., specimen GIT 426-1081, from Pirgu river outcrops, Raplamaa, Pirgu Regional Stage. F. Lateral view. G–H. Beloitoceras uuemoisense sp. nov., holotype GIT 1745-290, from Uuemõisa, Läänemaa, Pirgu Regional Stage. G. Lateral view. H. View of antisiphuncular side. I. View of prosiphuncular side. J. Adapical view. K–L. Multiceratoidea gen. et sp. indet. C, specimen GIT 878- 234, from Hosholm shore (tower), Vormsi Island, Pirgu Regional Stage. K. Adapical view. L. Lateral view. Scale bar = 10 mm in all figures except E, same scale in A–D, and in F–K. Scale bar in E = 5 mm.

Fig. 29. Median sections of phragmocones of Graciloceratidae Flower, 1950 and Oncoceratidae Hyatt, 1884 of the Vormsi–Pirgu regional stages, Estonia. A. Hiiumoceras hiiuense gen et sp. nov., holotype TUG 1745-11, from Paope quarry, Hiiumaa Island, Vormsi Regional Stage. B. Rizosceras teres sp. nov., paratype TUG 80-508, from Saxby shore, Vormsi Island, Vormsi Regional Stage. C. Beloitoceras siljanense Frye, 1987, specimen TUG 939-56, from Haapsalu holm, Pirgu Regional Stage. D. Dalecarlioceras constrictum Frye, 1987, specimen GIT 878-248, from Hosholm shore (tower), Vormsi Island, Pirgu Regional Stage. Scale bars = 5 mm.