Thracia convexa

(Wood W., 1815)

Description (shell):
Shell brittle, inflated, slightly inequivalve, right valve larger and more convex than the left. Inequilateral, beaks just behind the midline, directed inwards, the beak of the left valve sitting in a hole in the umbo of the right. Irregularly triangular in outline, somewhat drawn out posteriorly. Ligament external and internal; external ligament is thin behind the umbones; internal in a narrow pit immediately behind the beaks, not deeply concealed, the pit (resilifer) of the right shell is slightly thicker than that of the left. Lithodesma (often lost) in front of the ligament, very small and thin. Sculpture of irregular concentric lines and undulations on a finely granular surface with a smooth ridge running from the umbones to the posterior ventral corner. Hinge without teeth. In the left valve the dorsal line in front of the umbones is slightly turned inwards. Anterior adductor scar is long and thin, posterior scar triangular and thick. Pallial sinus is shallow.

Up to 63.5 mm in length.

White, rarely cream. Periostracum greenish yellow. Interior of shell white.

The shells gape behind to allow the extrusion of the separate siphons.

Lives in sand and mud offshore, though never in large numbers,

It is distributed from the Norwegian Sea south to the Mediterranean (Distr. T. convexa).