Thyasira ferruginea

(Locard, 1898)

Description (shell):
Shell is solid, equivalve, slightly inequilateral, beaks just in front of the midline, directed inwards and slightly forwards. Almost circular in outline. Ligament is small, concealed. Lunule and escutcheon are indistinct (T. ferruginea). Sculpture of very fine concentric lines beneath the covering deposit. Growth stages are indistinct. Hinge line is without teeth. Muscle scars are indistinct.

Up to 32 mm in length.

White or transparent beneath a thick rust coloured, encrusting deposit. Periostracum not visible. Inside of shell translucent reflecting the colour of the external deposit.

The thickened margin of the mantle is open all round and not prolonged into siphons. The long slender foot is almost cylindrical.

In mud and sandy mud, between 20-200 m.

In the northern North Sea (Distr. T. ferruginea). Elsewhere it is distributed from the Arctic, south to the Mediterranean and Madeira and to North Carolina and the Aleutians.