Terebratulina retusa ( Linnaeus, 1758 )

Terebratulina retusa ( Linnaeus, 1758) View in CoL

Figures 19 View Figure 19 , 20 View Figure 20

? Anomia aurita Linnaeus, 1758, p. 701 View Cited Treatment .

Anomia retusa Linnaeus, 1758, p. 701 View Cited Treatment .

Anomia pubescens Linnè, 1767, p. 1153 .

Terebratula pubescen s – Müller (1776), p. 249.

Anomia Caput serpentis – Born (1780), p. 119, pl. 6, fig. 13 – non Linnaeus (1758), p. 703 View Cited Treatment (see discussion in Hanley (1855) and Dall (1920)).

Terebratula caput serpentis – Retzius (1788), p. 13.

Terebratula retusa – Retzius (1788), p. 14.

Criopoderma caput serpentis – Poli (1795), p. 192 and 261, pl. 30, fig. 15y.

Terebratula aurita – Fleming (1822a,b), p. 498–499, pl. 4, fig. 5.

Terebratula costata Lowe, 1825, p. 105 –107, pl. 5, figs. 8, 9, 9b.

Terebratula emarginata Risso, 1826, p. 388 , pl. 12, fig. 175.

Terebratula quadrata Risso, 1826, p. 389 , pl. 12, fig. 176.

Delthyris spatula Menke, 1830 . p. 96.

Terebratulina caput serpentis – d’Orbigny (1847b), p. 248 –249, pl. 7, figs. 7, 8, 17.

Terebratula striata Leach, 1852, p. 359 , pl. 14, figs. 1–2.

Terebratula (Terebratulina) caput-serpentis – Lovell (1861), p. 172.

Terebratula caput-serpentis mediterranea Jeffreys, 1878, p. 401 .

Terebratulina retusa View in CoL – Dall (1920), p. 294.

Terebratulina retusa emarginata – Dall (1920), p. 296.

Description: Shell outline subpentagonal to nearly egg-shaped, and fully grown specimens generally with narrowly truncated or even incurved front. Anterior commissure gently to moderately uniplicate or, more rarely, rectimarginate. Ornamentation of 9–14 radiating, rather coarse costellate ribs per 5 mm counted 10 mm anterior of ventral umbo (occasionally up to 17 ribs). Ribs lacking on specimens less than 1 mm long, but rapidly become high and subangular, then weaken again with increased shell size. Ribs beaded with coarse tubercles on umbonal part, especially the ventral valve. In young specimens, these tubercles tend to partly overhang deep rib-interspaces along valve crest. Umbonal tip of ventral valve continuously becomes resorbed with growth, making umbo less pointed. Pedicle often strongly branched. Deltidial plates lacking or small and separate. Pedicle opening 11–13% as wide as valve. Shell matrix endopunctate. Colour white or yellowish-grey. Short brachial loop often, but far from always, with crural processes joining. Joined crural processes seem to be more common in larger specimens. Brachial loop not pointy in front. Median ridge absent or very rudimentary and restricted to posterior part of valve floor. Long setae radiating out from where ribs meet anterior valve margin. Soft tissue dense with spicules, especially in lophophores. Largest encountered was 26 mm long.

Depth range: 12–1492 m depth, though most common at 15–600 m depth ( Jeffreys 1878; this study). By mistake, the maximum depth was given as 1180 ft (~ 2157 m) by Jeffreys (1878), which was then quoted by others; however, in Jeffreys’ station table, the correct depth (1492 m) is given. However, since Jeffreys (1878) did not distinguish Terebratulina septentrionalis from T. retusa , the maximum depth could be for the other species. The maximum depth given Wesenberg-Lund (1938) distinguishing the two species is 1302 m.

Temperature range: 0.0–13.0˚C ( Curry 1982; Thomsen 2001). Jeffreys (1878) reported the species from several British samples, which, according to Carpenter et al. (1869), were taken at sub-zero temperatures down to -1.2˚C; however, Jeffreys did not distinguish the colder-water species Terebratulina septentrionalis from T. retusa .

Salinity range: 33.1–35.3 ( Nordgaard 1905; Thomsen 2001; this study).

Oxygen range: 77–105% saturation (this study).

Current velocity: Mean velocity measured at one locality was 9.5 cm /s, with daily maxima mostly 12–25 cm /s and 30 cm /s as the absolute maximum measured over 1 month (this study).

Substrate: Attached to bryozoans, hydroids, shells, sand, stones, Porifera, seaweeds, etc. ( Jeffreys 1863; Brunton & Curry 1979; Thomsen 2001; this study). Sea floor typically dominated by sand, shell sand, gravel, cobbles or stones ( Thomsen 2001).

Geography: Bjørnøya, Norway, Iceland, the Faroe Islands, SW Sweden, Great Britain, France, Spain, Portugal, the Mediterranean, the Canary Islands and the Cape Verde Islands ( Fischer & OEhlert 1892; Brunton & Curry 1979; Cohen et al. 1993; Thomsen 2001; Logan et al. 2007; this study). Neither the northernmost (Bjørnøya), easternmost two (Finnmark), nor all the records from the NW side of Iceland have been verified in the present study or in molecular studies.

Remarks: A comparison with the next and closely related Terebratulina septentrionalis is provided in the comments on that species.

The shells are often overgrown by a Demospongia of the genus Hymedesmia ( Tendal & Thomsen 2005) .

Plotting specimens according to the century of sampling did not reveal any changes in distribution within Norwegian waters. Despite the impression of the map, this species is only sporadically encountered along northern Norway.