(Montagu, 1803)
Description (shell):
Shell tumid, umbones just in front of midline. Broadly oval, almost circular. Sculpture of fine concentric lines, growth stages distinct. Lunule broad and shallow, escutcheon scarcely discernible. Right valve with a single cardinal tooth below beak of umbo, and single posterior lateral; left valve with two cardinal teeth below beak, and single posterior lateral. Small external ligament visible posterior to beaks; in each valve position of internal ligament is marked by embayment in hinge line posterior to cardinal tooth/teeth. Pallial line broad, ill-defined, adductor scars about equal, not distinct (K. suborbicularis-drawing).
Size:
Up to 10 mm long.
Colour:
White, with pale horn or yellowish periostracum. Inside of shell white or translucent.
Animal:
Nearly transparent. The mantle extends considerably beyond the shell margin, and its edges are united all round. There is a large opening on the lower margin to allow passage for the strap-shaped foot; it is greatly extended in front to form an incurrent tube, and a small opening behind serves as an excurrent siphon. The animal moves freely by means of its foot, and attaches itself by an almost invisible thread.
Habitat:
Distributed from the lower shore to at least 100 m; occurs in holes and crevices, within old shells, barnacle tests, etc. Most frequent on southern and western shores.
Distribution:
Distributed from Norway south to the Mediterranean and West Africa (Distr. K. suborbicularis).