(Philippi, 1845)
Description:
The outline is generally evenly rounded, height and length being almost equal, but some specimens may be somewhat pyriform. Adult specimens always have two distinct postero-dorsal folds or undulations, and the hinge margin is more thickened and stronger than in its relatives. Young specimens in which the undulations are less developed, are easily identified by means of their fairly conspicuous prodissoconch (T. gouldi).
Size:
Up to 9.0 x 9.3 mm.
Colour:
Some specimens have chestnut-coloured patches of precipitated material on their shells near the antero-dorsal and postero-dorsal margins.
Animal:
The thickened margin of the mantle is open all round and not prolonged into siphons. The long slender foot is almost cylindrical.
Habitat:
From a few metres below the shore line down to 385 m. The majority of the finds originate from depths less than 50 m. On various types of bottom. Most frequently, however, found on bottom consisting entirely, or partly, of clay or mud.
Distribution:
Panarctic, probably continuously circumpolar (Distr. T. gouldi).