Cuspidaria rostrata

(Spengler, 1793)

Description (shell):
Shell is brittle, almost equivalve, the left valve just slightly more convex than the right one. Inequilateral, beaks in the anterior half, directed inwards, touching. Broadly oval in outline with a long projecting posterior spout with a terminal gape; this spout can be almost as long as the rest of the shell. Ligament is internal, in a small triangular chondrophore immediately below the beaks, with a small embracing lithodesma. Sculpture is faint, of very fine lines. A thin ridge runs from the umbones to the posterior margin of the spout. Growth stages are not clear. Right valve with a small ridge-like posterior lateral tooth which fits under a ventral projection on the posterior dorsal line of the left valve. There are no cardinal teeth. Adductor muscle scars are small, about equal. Pallial line with a slight indentation where it crosses the beginning of the spout. Margin is smooth.

Up to 25.5 mm in length.

White. Periostracum cream. Inside of shell white (C. rostrata).

The siphons are relatively short and the hinder part of the shell is drawn out to partially cover them; their orifices are protected by long tentacles whose ends are divided into several finger-like points. The Cuspidarians are the only truly carnivorous bivalves. The gill is a muscular septum and the pumping and sucking action of this draws in food consisting mainly of dead crustacea.

It is widely distributed, however, across the north Atlantic from the Arctic to the West Indies and northern Norway south to the Mediterranean, the Atlantic coast of Morocco, the Canary Isles, the Azores and to Sierra Leone and Liberia (Distr. C. rostrata).