Hemithiris psittacea ( Gmelin, 1791 )

Hemithiris psittacea ( Gmelin, 1791) View in CoL

Figures 1A, 1B, 1F, 1J View Figure 1 , 9 View Figure 9 , 10 View Figure 10

Anomia rostrum psittaci Chemnitz, 1785, p. 106 , pl. 78, figs. 713a–b. Anomia psittacea Gmelin, 1791, p. 3348 .

Lampas psittacea – Calonne & Humphreys (1797), p. 45.

Terebratula psittacea – Lamarck (1819), p. 248.

Gypidia psittacea – Menke (1830), p. 96.

Hypothyris psittacea – King (1846), p. 28.

Hemithiris psittacea View in CoL – d’Orbigny (1847b), p. 246.

Rhynchonella psittacea – Davidson (1852a), p. 251 –253, pl. xiii, figs. 1a–b.

Rhynchonella ( Hemithyris) psittacea – Dall (1873), p. 196.

Description: Shell with subtriangular or subpentagonal outline and rather acutely pointed beak. Large specimens approximately as wide as long. Anterior commissure uniplicate on specimens larger than 16 mm, while gently unisulcate on specimens smaller than 4 mm. Lateral valve commissure unevenly curved. Ornament developing from 1.2–4 mm valve length and outwards as fine, broad and very flat radiating ribs or relatively well-separated striae. Shell matrix impunctate. Colour dark bluish, dark grey or brownish except in small specimens, which are light-coloured and transparent. Ventral umbo beak-shaped and rather long. Rudimentary triangular deltidial plates not joining but forming a roughly U-shaped pedicle opening. Distinct pedicle collar. Elongate, unbranched pedicel. Small specimens with setae protruding as prolongation of striae. Well-developed dental plates. Crura flattened. Weak and short dorsal median ridge. Maximum length 30.4 mm.

Depth range: 0–2078 m depth, though rarely found deeper than 400 m, and only two reports from deeper than 1000 m depth (Cooper 1973a; this study).

Temperature range: -2–12˚C ( Knipowitsch 1901; Ullmann et al. 2017).

Salinity range: 26.2–35.5 ( Zezina 2008; this study).

Oxygen range: Oxygen saturation 83–105% (this study).

Current velocity: Mean current velocity of 2.6–11.7 cm /s, with daily maxima of 4–30 cm /s and an absolute maximum velocity of 13.3–72.2 cm /s over 1 month of measurement (this study).

Substrate: Usually attached to small pebbles, shells or rocks, but can be attached to any kind of hard surface such as serpulid and Nothria tubes, bryozoans, Cirripedia fragments, rhodoliths or even Foraminifera and sand grains (this study). Found on mud- or sand-dominated sea floors mixed with shell sand, or on gravel, pebbles, stones, calcareous red algae, rock grounds or vertical cliffs (Leche 1878; Posselt 1898; Arndt & Grieg 1933; Wesenberg-Lund 1940a,b; Thomsen 2012; this study).

Geography: Arctic Ocean, E and W Canada, E and W Greenland, Svalbard, Jan Mayen, Kara Sea, Laptev Sea, the White Sea, Norway (from Folda in Nordland and north), S and W of Iceland, W USA, and Japan (e.g., Posselt 1898; Lamy 1913; Grieg 1933; Brunton & Curry 1979; Zezina 1997b, 2008; this study).

The species is also reported from the North Sea, Faroe Islands, at the Hebrides, Ireland, Orkney Isles and Shetland Isles (e.g., Lyell 1842; Dall 1920; Brunton & Curry 1979; Thomsen 2001). Following Jeffreys (1863, 1878) and based on specimens examined at the Natural History Museum of London, all certain observations around the British Isles are empty and likely of glacial age. The reported presence at the Faroe Islands by Lyell (1842) was based on the apparent glacial material (BMNH PI ZB 1667). Additionally, according to Thomsen (2001), there are no other possible recent specimens known from the area.

Jeffreys (1878) mentioned the species from Drontheim (=Trondheim) in Trøndelag, Norway, while Wesenberg-Lund (1939) reported it from Brettingsnes in the Trondheimsfjord. However, the latter are two empty shells most likely of glacial age. The first was a re-occurring mistake that Jeffreys (1869b: 164) admitted, using Trondheim instead of Tromsø.

Dall (1920) listed a specimen from Bergen in Vestland, Norway. According to the collection list, the University Museum of Bergen also houses a specimen from that area. However, the latter was missing, and both are most likely not recent shells.

In the collections housed at the Natural History Museum of London was a single specimen collected alive ( BMNH PI B 24769 ) with no other information than ‘ North Sea’ . The label dates it to before the year 1900. However , it seems more likely that the information is incorrect rather than the specimen actually is originating from the North Sea.

Remarks: The species was first named, described and beautifully illustrated by Chemnitz (1785). However, since he used a trinomial name instead of the Linnean binominal system, Gmelin (1791) is accepted as having named the species.

Within Norwegian waters, it seems that this Arctic and subarctic species has been retreating northward within the last century since no live specimens appear to have been collected south of 69.2°N in Nordland and Troms after 1923, while it was collected from several localities south to 67.6°N before then.

Despite its wide depth range, Hemithiris psittacea is primarily associated with coastal environments.