KRAUSSINIDAE Dall, 1870

Hansen, Jesper, 2024, Brachiopods of the Norwegian fauna northern North Atlantic and Arctic, with a focus on, Fauna norvegica 43, pp. 12-68 : 48-51

Family KRAUSSINIDAE Dall, 1870 Genus Megerlia King, 1850

Remarks: The validity of the three species Megerlia truncata , M. monstruosa and M. echinata has been a matter of debate for the last nearly 200 years, with many of the greatest brachiopodologists in history taking opposite views. As the issue is still not settled, I feel it is necessary to give an overview of the history of these species. Already, when erecting M. monstruosa, Scacchi (1833) admitted doubt, whether the specimen of his new species in reality was the species M. truncata , which just had shaped itself after the substrate. This opinion of synonymy was shared among others by Costa, Monterosato and Jeffreys based on the internal features, though Jeffreys kept the species as a variety of M. truncata (see: Costa 1838; Monterosato 1872; Jeffreys 1878). Davidson (1887) followed the lead of the others but observed that all specimens he had encountered of M. monstruosa differed in a uniform way from M. truncata , why he chose to keep it as a variety. Subsequently, Fischer & OEhlert (1890) erected a very similar species, M. echinata , mainly differing by having minute spines on the surface. They then followed up by restoring M. monstruosa to the nature of the micro-ornament differed from that of M. truncata , species level arguing that while M. truncata often showed deformation why they concluded M. echinata is a valid species distinct from M. due to confinement of substrate, the degree of deformation in shells truncata . of M. monstruosa was so extreme and consistent, like the mode of At present, it seems that the greater majority consider both M. convexity; ornamental characteristics; narrower shell; pedicle opening monstruosa and M. echinata synonymous with M. truncata , while a moved into dorsal valve; the smaller interarea; and the cardinal area large minority consider M. echinata a valid species. on the inside, that they were species-specific ( Fischer & OEhlert 1891). The division in the present work is based on the following Dall (1919 and 1920) found the shared feature of the pedicle opening reasoning. On a general basis when assuming two species are allocated to the dorsal valve warranted, that M. echinata and M. synonymous, it would be expected that the various features show monstrousa with M. monstruosa as type species were moved into a more intermediate forms as of the type form of the least common new genus Pantellaria . Based on observed variability within Megerlia form group. Similarly, it would seem unlikely to encounter a truncata, Thomson (1927) questioned the validity of the suggested relatively consistent combination of seemingly uncorrelated features generic differences as more than species-level differences. Atkins differentiating two subgroups within the species if no external barriers (1961a) followed up with a study on M. echinata . There she did not keep populations separate over an extended time. find support for separating this species, but lacking specimens for Going through the available material of the genus, there turned the study of M. monstruosa , did not suggest transferring that back as out to be two distinct form groups for which I did not manage to well. Most accepted the transfer, though some maintained Pantellaria find intermediates among the probable nearly 1000 specimens I have for M. monstruosa long after (e.g.: Cooper 1981a, 1982; Zezina 2010, seen. The biggest group contained specimens rather conservatively 2014). While noting M. monstruosa externally closely resembled biconvex and unisulcate, with the major part of the pedicle opening species of the genus Platidia, Logan (1979) again put M. monstruosa in the ventral valve, and with both valves exhibiting dense, finely into synonymy with M. truncata , though not providing a discussion costellate ribs as well as low tubercles. Deformation in these on why. Comparing the specimens of M. echinata from Atkins (1961a) specimens appeared only to occur in cases where the specimens had with those of M. monstruosa used by Davidson (1887), Brunton (1988) been cramped by substratum or damaged during life. This form group disagreed on this synonymy and argued that M. monstruosa and M. has the typical shape of M. truncata . echinata were synonymous though distinct from M. truncata . He thus The smallest group contained the specimens with dorsal valve placed them under the senior name M. monstruosa , an opinion which typically nearly plane to concave, shaping itself after the substratum was followed by Anadon (1994). His study seems to be rather unique and rarely showing any hint of ornament other than growth lines; a in that it directly compared the two species and did not just give a convex ventral valve with sparse and uneven, weak costellae with discussion on how each of them differed from M. truncata . scattered tubercles, as well as variably developed minute and alveolate

Just two years later, Bitner (1990) published a study on 13–16 thorns and spines; and a pedicle opening moved almost entirely into million-year-old Middle Miocene Polish fossils. Though she did not the dorsal valve in mature specimens. Specimens still attached to their find specimens fully resembling M. echinata and M. monstruosa substrate, showed that the odd shape was not due to confined space among her more than 2500 specimens, she did have intermediate or shell damage during life. The shape and the minute spines place specimens and thus concluded, that all three species were one and this form group as M. echinata . I was unable to find any evidence of the same. In general, I hesitate to put too much weight on using the external reasons for the general shape of the specimens of M. echinata . shell morphology of so old specimens as a proof of species synonymy I thus find myself in support of the opinion, that M. echinata is not of living brachiopods. This is because 15 million years is a very synonymous with M. truncata , and therefore chose to keep them long time for a species, and both the morphology, and the degree of separate in this publication. morphological variability, can change significantly over such a time Another observation from this study was how unevenly distributed span, as well as that species can split up in a shorter time (e.g.: Sheldon the minute thorns and spines were developed on the ventral valve of 1987; Wei & Kennett 1988). Nonetheless, this publication became an many of the examined specimens in the form group of M. echinata . important basis for changing the major opinion towards the existence These spines were evenly and densely distributed on some valves, of only one species. Interestingly, in a simultaneous study on nearly while only present on parts of valves or nearly lacking on others. 1000 specimens from the same Polish deposits, Barczyk & Barczyk Specimens lacking these spines fit in both shape and ornamentation (1990) came to the opposite conclusion, that they had two distinct the description of M. monstruosa and I therefore feel inclined to think species, M. truncata and M. monstruosa . Barczyk & Barczyk (1990) that Brunton (1988) and Anadon (1994) were right in that the two found the differences so distinct and ontogenetic stable, that they species are synonymous rather than M. monstruosa with M. truncata . preferred to follow the opinion of generic division of the two species. However, I here realise there are strong opinions to the contrary, and

With supporting observations of recent morphologically as I have not seen the type specimen of M. monstruosa , I leave this intermediate specimens, Logan et al. (2004) agreed with Bitner question for others to clarify. If, however, the two species turn out to (1990) that evidence points to M. monstruosa being conspecific with be synonymous, the name M. monstruosa is the senior synonym. M. truncata , though they recognized it as a variety and accepted M. echinata as a valid species. This opinion on synonymy was followed by Anadon et al. (2022), Logan (2007), and Logan et al. (2007, 2008). Megerlia echinata ( Fischer & OEhlert, 1890) Others, like Alvarez & Emig (2005), Hiller et al. (2008), Alvarez Figures 46 , 47 (2016) and Emig (2016), were more inclined to agree with Bitner (1990) in that all three species are synonymous. Trying to give a better? Terebratula monstruosa Scacchi, 1833, p. 17 . basis for comparison, Simon et al. (2016) provided SEM pictures of? Megerlia truncata var. monstruosa – Davidson (1887), p. 108, pl. 9, figs. the holotype of M. echinata together with a discussion. They found 21–22.

Mühlfeldtia echinata Fischer & OEhlert, 1890, p. 73 –74.

? Mühlfeldtia monstruosa – Fischer & OEhlert (1891), p. 87 –90, pl. 7, figs. 12a–c.

Pantellaria echinata – Dall (1919), p. 251.

? Pantellaria monstruosa – Dall (1919), p. 251.

Megerlia echinata – Atkins (1961b), p. 89 –94.

? Megerlia monstruosa – Brunton (1988).

Description: Shell low, ventribiconvex to concavoconvex and typically taking shape after the substrate that the dorsal valve is lying on. Adult specimens transverse oval to subrectangular. Umbo blunt and very broad. Narrow and slightly unisulcate anterior commissure in less deformed adults, but rectimarginate in juveniles. Hinge line straight. Narrow deltidial plates not joined. Very large and subcircular pedicle opening almost entirely located in dorsal valve. Ornamentation on ventral valve of generally widely spaced, unequal, uneven, fine and rather poorly defined costellae with scattered tubercles. Minute alveolate thorns or spines usually on and between costellae, though often unevenly distributed and may be lacking entirely. Surface of dorsal valve usually just marked by coarse growth lines, but very weak and sporadic costellae may occur. Shell matrix endopunctate. Colour yellow or white. Dorsal interior with long brachial loop reaching 2/3 valve length and supported by median septum. Lophophoral filaments approximately as long as or longer than 1/2 shell length. Dorsal septum extending to approximately mid-valve length of shell. Inner surface of valves with radiating lines of tubercles, especially strongly developed in a broad submarginal rim. Maximum shell size 13.5 mm long and 18.5 mm wide.

Depth range: 10–2780 m depth ( Koskeridou 2007; Logan 2007). However, after excluding geographically isolated reports and certain misidentifications of the species, the depth range narrows to 128–2780 m, making it a moderately deep- to deep-water species ( Koskeridou 2007; Simon et al. 2016; Anadón et al. 2022).

Temperature range: 9.5–13.6˚C (this study).

Substrate: Attached to corals ( Dendrophyllia ramea and Desmophyllum pertusum ) or shells ( Costa 1838; Fischer & OEhlert 1891; Massy 1916; Atkins 1961c). This species usually seems to be associated with corals.

Geography: Along the shelf edge of the Celtic Sea and the Bay of Biscay, off Portugal and West Sahara, as well as in the Mediterranean Sea ( Jeffreys 1878; Fischer & OEhlert 1890; Massy 1916; Dall 1920; Atkins 1961c; Gaspard 2003). Observations were also reported from Florida, the Caribbean, the Cape of Good Hope, the Red Sea and SE Australia ( Dall 1920; Cooper 1981b; Logan et al. 2008); however, those from the Red Sea were later recognised as a new species within another genus by Simon et al. (2016), while the remainder are more likely representatives of other species.

Remarks: See the above remarks for the genus concerning synonymy for the species. The present study was based mostly on the collection housed at the Natural History Museum of London, including numerous specimens of M. truncata and many specimens and even populations assigned to both M. echinata and M. monstruosa .

Figures

Figure 46. Megerlia echinata. a: ventral view of specimen in batch BMNH PI ZB 4258–4259, near Tunis, Tunisia, Mediterranean; b: dorsal view of specimen in batch BMNH PI ZB 4258–4259, near Tunis, Tunisia; c–e: dorsal and ventral views, as well as close-up details of spiny ornamentation on ventral valve of specimen in batch BMNH PI ZB 2721–2723, Sardinia, Italy; f–i: dorsal, ventral, lateral (with ventral side up) and posterior views of specimen from batch BMNH PI ZB 4975, southern Celtic Sea, 585–896 m; j–l: ventral, lateral (with ventral side up) and anterior views of specimen from batch BMNH PI ZB 4975, southern Celtic Sea, 585–896 m; m–n: ventral and anterior views of large specimen from batch BMNH PI ZB 4975, southern Celtic Sea, 585–896 m. Scalebar 1mm. Photos: Jesper Hansen.

Figure 47. Distribution of Megerlia echinata.