Thracia papyracea

(Poli, 1791)

Description (shell):
Shell is brittle and inequivalve, right valve a little more convex than the left, the beak of one valve often punctures the other valve. Inequilateral, beaks are behind the midline. Approximately oval in outline with the dorsal posterior line straight, and the posterior margin truncate and slightly gaping. Ligament external and internal; external wide and small, immediately behind the beaks, with the internal element in a triangular resilifer immediately below it. Lithodesma (often lost) is short and broad, attached to the valves directly in front of the ligament pit. Sculpture of smooth concentric lines and ridges on a very finely granulated surface. Immediately behind the beaks, between a shallow posterior umbonal ridge and the posterior dorsal line, this granular surface is rather coarse but elsewhere, over the main body of the shell, it is exceedingly fine and smooth, almost velvet-like to the touch, the granulations appearing clearly under the microscope only at magnifications greater than x 20. Hinge is without teeth. Anterior adductor scar is thin, posterior scar fat. Pallial sinus deep reaching a position below the resilifer (T. papyracea-drawing).

Up to 38 mm in length.

Interior of shell white.

The animal varies in colour from white to pale brown. The foot has a bluish tinge. The shells gape posteriorly to allow the extrusion of the siphons. These are short and wide, marked at their extremities with faint lines.
(T. papyracea-animal).

In sand, muddy sand and sandy gravel from very low in the intertidal zone to about 55 m.

Because of the difficulty in correctly identifying this species the extent of its geographical range is uncertain, but it probably extends from northern Norway to the Mediterranean and Black Sea and along the Atlantic coast of Morocco and to Madeira (Distr. T. papyracea).