Cryptopora gnomon Jeffreys, 1869a

Hansen, Jesper, 2024, Brachiopods of the Norwegian fauna northern North Atlantic and Arctic, with a focus on, Fauna norvegica 43, pp. 12-68 : 24-25

Cryptopora gnomon Jeffreys, 1869a

Figures 7 , 8

Cryptopora gnomon Jeffreys, 1869a, p. 136 .

Atretia gnomon – Jeffreys, in Carpenter et al. (1869), p. 421. Dimerella gnomon – Dall (1873), p. 197.

Neatretia gnomon – Fischer & OEhlert (1891), p. 122–125, figs. 11a–c. dominated by sand, shell sand, gravel, cobbles and/or rock ( Thomsen 2001), though visual surveys indicate this is a bias reflecting the sampling methods ( Toma et al. 2022; this study).

Geography: Svalbard, Norway (but rare in NE Finnmark), Iceland, the Faroe Islands, Greenland (a live specimen collected on the west coast and one empty shell from the SE coast), SW Sweden, Great Britain, France, Spain, Portugal, the Mediterranean, Azores, Morocco, Cape Verde, Madeira, the Canary Islands, the Mexican Gulf and the Caribbean ( Robinson 2017; this study) ( Figure 6 ).

Remarks: No live specimens appear to have been collected around Svalbard before 1900; however, this is likely reflecting the sampling methods.

Description: Shell low to moderately biconvex. Outline subpentagonal to subtriangular with small, beak-shaped, acute umbo. Anterior valve commissure slightly unisulcate and lateral commissure gently S-shaped. Scattered short setae along valve margins. Dorsal sulcus broad, weak and restricted to the front. Ornamentation normally lacking, but weak striation from the growth tracks of setae attachments along valve margin can develop on larger specimens. Shell matrix impunctate. Shell thin, transparent and colourless or slightly yellowish. Pedicle opening triangular and deltidial plates rudimentary. Pedicle orange and varies from long and tread-like to short. Attachment end of pedicle with short rootlets. Dental plates extend to approximately 1/4 valve length. Dorsal median septum long, shark fin-like, high and thin, starting close to umbo and extending to between 1/2 and 2/3 valve length. Crura delicate, anteroventrally directed and moderately long, with lophophores extending to about mid-valve length. Maximum length 6 mm.

Depth range: 520–4390 m depth and mostly from deeper than

Substrate: Attached to sand grains, rocks, foraminiferan sand tubes and other hard surfaces on mud-dominated sea floors ( Posselt 1898; Brunton & Curry 1979; this study).

Geography: Arctic Ocean off Graham Bell Island in the archipelago of Franz Josef Land, West of Bjørnøya, Norway (Nordland and Troms, and possibly also South to Vestland), Iceland, W Greenland, E Canada, Atlantic Ocean, Ireland, eastern USA, Azores, Morocco, Cuba, the Caribbean, and Panama ( Fischer & OEhlert 1891; Posselt 1898; Dall 1920; Wesenberg-Lund 1939, 1940a; Cooper 1973a; Zezina 1997 a, 2008, 2014; Thomsen 2012).

The species is also reported from the Falkland Islands in the SW Atlantic, off South Africa, and as empty shells from the Tasman Sea at Macquarie Island, S of New Zealand ( Cooper 1973a; Zezina 2008, 2010, 2014). Although the shell morphology is very similar, these specimens require a rigorous examination since they are, as already pointed out by Cooper (1973a), very far outside the normal known distribution of the species.

Based on the available coordinates, this deep-water species appears to prefer the shelf edge, slope and abyssal marine environments.

1000 m ( Posselt 1898; Zezina 2010). Specimens sampled at 35–450 m depth in Norway, Iceland, Greenland and the USA have also been referred to as this species (e.g., Dall 1920; Wesenberg-Lund 1938, 1939, 1940a, 1941). However, since one-third of these were located and examined at the visited museums and all turned out to be juvenile shells of Macandrevia cranium and Hemithiris psittacea , the rest are presently considered doubtful.

Temperature range: -1.2–3.4˚C (this study).

Salinity range: 32.3–35.1 ( Wesenberg-Lund 1940a; Thomsen 2012; this study).

Figures

Figure 6. Distribution of Novocrania anomala.

Figure 7. Cryptopora gnomon. a–d: four specimens, Davis Strait, W Greenland, ‘Ingolf’ expedition st. 36, 2702 m; e–h: dorsal, oblique ventral view with septum visible, lateral and anterior view of a shell, Eggagrunnen, Nordland, Mareano 2008 st. R297-347B, 808 m; i–j: ventral view of a specimen and dorsal view of an empty shell, Eggagrunnen, Nordland, Mareano 2008 st. R297-347B, 808 m; k: dorsal view of specimen, Eggagrunnen, Nordland, Mareano 2008 st. R297-346, 807 m. a–d: Natural History Museum of Denmark, Zoological Museum of Copenhagen. e–k: collected by the Institute of Marine Research and housed at the University Museum of Bergen. Photos e, i, j and k: Katrine Kongshavn. Scalebar 1mm. Photos a–d, f–h: Jesper Hansen.

Figure 8. Distribution of Cryptopora gnomon. Doubtful observations in need of verification are marked as such.