(Montagu, 1808)
Description (shell):
Shell is fragile, equivalve and inequilateral, beaks in the posterior half directed inwards. Outline is regularly oval. Internal ligament below and behind the beaks extending inside, below the umbones (T. ferruginosa-hinge). Underneath the deposit of periostracum the sculpture is of concentric lines and a very few, very faint radiating lines. Growth stages are clear. Right valve with one cardinal tooth its base continuous with a low ridge. Left valve with one anterior lateral. There are no posterior lateral teeth in either valve. Anterior adductor scar is larger than the posterior. Pallial line is wide. Margin is smooth (T. ferruginosa-drawing).
Size:
Up to 7.9 mm in length.
Colour:
White. Periostracum is thin, often covered by a thick rust-coloured deposit. Inside of shell white, sometimes tinted light purple.
Animal:
One large siphonal tentacle above, the orifice of the exhalant siphon below. Numerous and densely placed papillae along the ventral part of the middle fold of the mantle.
Habitat:
Particularly in fine muddy sand. A common commensal of Echinocardium cordatum , one of the sand-burrowing echinoderms.
Distribution:
In the whole North Sea (Distr. T. ferruginosa). Distributed from northern Norway, south to the Mediterranean, along the Atlantic coast of Morocco and to Madeira.