Glaciarcula spitzbergensis ( Davidson, 1852c )

Hansen, Jesper, 2024, Brachiopods of the Norwegian fauna northern North Atlantic and Arctic, with a focus on, Fauna norvegica 43, pp. 12-68 : 42-43

Glaciarcula spitzbergensis ( Davidson, 1852c)

Figures 1D, 1H , 34 , 35

Terebratella spitzbergensis Davidson, 1852c, p. 78 –79.

Terebratula (Terebratella) spitzbergensis – Lovell (1861), p. 178. Magasella spitzbergensis – Dall (1870), p. 137.

Terebratalia spitzbergensis – Dall (1920), p. 347.

Diestothyris (?) spitzbergensis – Thomson (1927), p. 244.

Diestothyris spitzbergensis – Helmcke (1938), p. 252.

Glaciarcula spitzbergensis – Elliott (1956).

Description: Shell egg-shaped. Rectimarginate anterior commissure. No ornamentation except irregular growth lines. Shell matrix endopunctate. Colour yellowish white. Umbo long, curved and beak-shaped, except in specimens below 3.5 mm long. Pedicle opening very elongate. Deltidial plates usually not joined and rudimentary in small specimens. Pedicle commonly strongly branched. Ventral teeth supported by dental plates. Long pedicle collar (thickening of valve floor) extending to front of dental plates. Dorsal median septum in subadult and adult shells triangular and reaching from umbo to approximately 3/5 to 2/3 valve length and terminating gradually. Juveniles below 3 mm long with a short, more pedestal-like septum. Brachial loop long. Maximum shell length 13.3 mm.

Depth range: 26–547 m depth ( Friele & Grieg 1901; this study), mostly from the shelf seas at 40–400 m depth. This species was described by Wesenberg (1940a, 1941) from several samples collected deeper than 1000 m. However, a re-examination of the specimens revealed them to be Cryptopora gnomon or juvenile Macandrevia cranium .

Temperature range: -2–3.8˚C ( Knipowitsch 1901; Grieg 1933; Ullmann et al. 2017).

Salinity range: 32.5–35.1 ( Wesenberg-Lund 1940a; this study).

Substrate: Attached to sand grains, gravel, Sessilia shells, polychaete tubes or bryozoan branches (this study). Found on muddy or sandy bottoms with annelid tubes or gravel ( Posselt 1898; Knipowitsch 1901, 1902; Grieg 1933).

Geography: Arctic Ocean, N Canada, Greenland, Beaufort Sea, Chukchi Sea, Laptev Sea, Kara Sea, Svalbard, Barents Sea, Norway (Finnmark), N and E Iceland, and Japan (e.g., Jeffreys 1878; Posselt 1898; Derjugin 1915; Grieg 1933; Zezina 1997a,b; Thomsen 2001; Ullmann et al. 2017).

The species is also found in glacial deposits from SW Sweden, the Shetland Islands and the Oslofjord ( Lyell 1835 (as Terebratula ); Jeffreys 1869b; Davidson 1887).

Three specimens collected by Jeffreys and reported by Davidson (1887) from three stations on the slope at the Western Approaches and from just SW of Portugal have been assigned to this species. The bottom-water temperatures at these stations were 9, 10 and 11.5˚C, respectively ( Jeffreys 1878), and thus far higher than where the species otherwise occurs. However, Jeffreys (1878) noted that he did not find any individuals of that species, but had initially misidentified a juvenile Dallina from one of the two northern stations. In fact, the specimen (BMNH PI ZB 790) was a Fallax dalliniformis , which, as a juvenile, is easily confused with Glaciarcula spitzbergensis . The other northern specimen (BMNH PI ZB 4946) was an empty valve of a new species, Dallina lusitanica . Moreover, Brunton & Curry (1979) misread Davidson (1887) and assumed that these two stations were at the Scilla Isles.

Glaciarcula spitzbergensis was reported from two places at Trondheim by Wesenberg-Lund (1939); however, both of these finds turned out to be juvenile Macandrevia cranium . The same occurred for the specimens from the Faroe Islands and most of those from Iceland reported by Wesenberg-Lund (1938, 1940a,c, 1941).

Three specimens, which, according to their label are from the Haltenbank off western Norway, are housed at the University Museum of Bergen. However, since there are some information disagreements between labels and information published by Grieg (1933) (he had assigned finds from that locality to the species Hemithiris psittacea ), it is likely that the label does not belong to the specimens .

Remarks: When comparing new and old observations of this Arctic species, it cannot be excluded that the southern limit of the species is shifting further north, away from Norway.

Figures

Figure 1. Terminology used in the paper. d–g show different shapes of the anterior commissure. Species shown: Hemithiris psittacea (a, b, f, j); juvenile Terebratulina septentrionalis (c); Glaciarcula spitzbergensis (d, h); Dallina septigera (e, g); Macandrevia cranium (i).

Figure 34. Glaciarcula spitzbergensis. a–d: dorsal, lateral, (close-up) surface and anterior views of specimen, Rijpfjorden, Spitsbergen, RV ‘Jan Mayen’ 2009 st. 67, 168 m (JH); e–f: dorsal and ventral interior views of glacial shell BMNH PI ZB 2763, from raised beach at Uddevalla, Bohuslän, Sweden; g–i: interior and oblique internal views of dorsal valve, and ventral valve interior of shell TSZBr-2409, Jarfjord, Finnmark, Norway, 110 m. Scalebar 1mm. Photos: Jesper Hansen.

Figure 35. Distribution of Glaciarcula spitzbergensis. Colours mark which century the specimens were collected in, as well as the dubious observation.