Axinulus aff. croulinensis Jeffreys, 1847

Oliver, P. Graham, 2015, Deep-water Thyasiridae (Mollusca: Bivalvia) from the Oman Margin, Arabian Sea, new species and examples of endemism and cosmopolitanism, Zootaxa 3995 (1), pp. 252-263 : 259

Axinulus aff. croulinensis Jeffreys, 1847

Fig. 4A

Material. Two specimens, Off Ras Madrakah, southern Oman, Discovery cruise 211 st. 12719#1, 19°08´N 58°39´E, 3150 m, collected P.G. Oliver, 31 October 1994. NMW.Z. 1995.009.18.

Description. To 2 mm in height. Very thin shelled. Equivalve. Equilateral. Outline almost circular a little higher than long; anterior dorsal margin very short, horizontal; anterior curved, ventral slightly extended, posterior curved; posterior dorsal short sloping gently. Hinge plate smooth, edentulous.

Remarks. In every respect these shells are identical with A. croulinensis from the Atlantic Ocean ( Fig. 4 B). In the Atlantic A. croulinensis has been recorded throughout and from depths a little as 40 m to 3861 m ( Payne & Allen 1991). Zelaya (2010) separated off the Antarctic populations as A. antarcticus Zelaya, 2010 but from shell characters there is little difference. The Atlantic abyssal A. brevis ( Fig. 4 E) has a more tear-drop shaped shell with a distinct anterior slope while an undescribed species ( Fig. 4 C) from the Gulf of Mexico is distinctly oblique. Other species cited in WoRMS under Axinulus do not conform and need reassignment or placed in as yet undescribed genera. The genus Genaxinus is distinct with the very characteristic elevated adductor scars with species known from the Atlantic and SE Australia; Genaxinus eumyarius M. Sars, 1870 and Genaxinus albigena Hedley, 1907 . Axinulus careyi Bernard, 1979 has the appearance of a Mendicula and Axinulus hadalis ( Okutani, Fujikura & Kojima, 1999) and Axinulus thackergeigeri Valentich-Scott & Coan, 2012 in Coan & Valentich-Scott, 2012 require novel placement.

Figures

FIGURE 4. A, Axinulus aff. croulinensis, Oman margin; B, Axinulus croulinensis Jeffreys, Loch Fyne, 40 m, Scotland, National Museum Wales; C, Axinulus undescribed, Gulf of Mexico, National Museum Wales; D, A. brevis Verrill & Bush, Rockall Trough, 1595 m, National Museum Wales; E – F, Mendicula aff. ferruginosa, Oman margin; G – H, Mendicula ferruginosa Forbes, Rockall Trough, 1595 m, National Museum Wales; I, Leptaxinus indusarium Oliver & Levin, holotype, National Museum Wales, NMWZ. 2005.34.1.