Axinulus Verrill & Bush, 1898

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 : 258-259

Axinulus Verrill & Bush, 1898

Type species. Cryptodon (Axinulus) brevis Verrill & Bush, 1898

Diagnosis. Very small, <5 mm. Equivalve. ~Equilateral. Outline oval, slightly higher than long, margins entire, lacking any sinus but with weak angulation of the posterior margin in some. Lunule, auricle and submarginal sulcus all indistinct; posterior sulcus absent. Hinge plate smooth. Ctenidium of a single demibranch (Type 2bR of Oliver, 2014), foot vermiform, lateral body pouches simple without or with a few indistinct lobes.

Remarks. This genus is distinguished by its small size, unremarkable shells, and single demibranch condition, the latter the most useful for distinguishing it from small species assigned to Thyasira , which retain both demibranchs. Other species with a single demibranch can be assigned to Adontorhina or to Mendicula . In both the shell is transversely oval, Adontorhina species distinguished by the presence of microscopic crenulations along the hinge plate.