Linné, 1758
Description (shell):
Shell thin and fragile. Anterior lobe triangular, with fine horizontal ridges; anterior disc with fine vertical to oblique ridges; median disc narrow, concave, with concentric sculpture; posterior disc with fine concentric lines; auricle semi-elliptical, almost as large as anterior lobe. Both valves strongly convex. Umbonal reflection closely applied to umbo; posterior hinge line broad, concave, with a bounding ridge. Junction of auricle with posterior disc visible as a ridge on the inner surface, median disc generally indistinct. Apophysis long, curved, slender, and rod-like, extending two-thirds of the depth of the shell. A knoblike condyle below the umbone and another on the opposite, ventral, border. Pallet blade elliptical with a concave edge, handle short, cylindrical, not extending on to blade (T. navalis-detail).
Size:
Up to 10 mm long.
Colour:
White, periostracum light brown. Inner surfaces white.
Animal:
Worm-like animal with enormously developed siphons. For the protection of the body a chalky tube is secreted. At the mouth of the tube, the animal has developed a pair of accessory valves - pallets - the handles of which are attached to the body. The oval blades of the pallets serve to close up the tube when the siphons have been withdrawn.
Habitat:
The borings are frequently found in drifted, waterlogged wood, each lined with a thin tubular, calcareous deposit (T. navalis-borings).
Distribution:
Widespread around the world (Distr. T. navalis).