(Adams J., 1797)
Description (shell):
A moderately tall conical shell of 5-6 whorls. The whorls dip sharply to the sutures but are otherwise only gently curved. Apex is blunt with intucked larval shell. There are 20-25 costae on the last whorl, tending to be flexuous and ending at the periphery and not reaching the base; mainly orthocline. The costae are flat-topped and about equal in breadth to the intervening hollows. Usually there are two spiral ridges near periphery of the last whorl, one on each whorl in the spire. Umbilical groove usually ends in a chink. Tooth is usually obvious on columella. The outer lip has a slight anal sinus and peripheral projection. Last whorl occupies about 60 % of shell height, aperture 35-40 %.
Size:
Up to 3 x 1.5 mm.
Colour:
White.
Animal:
The head has two more or less triangular tentacles longitudinally grooved along their lateral margins, with their bases almost linked across the midline. The eyes are small and close together between the tentacle bases. A short and narrow mentum projects from under the tentacles with the proboscis opening at its base dorsally. The opening of a sac into which the penis is invaginated lies between the mentum and the dorsal surface of the foot. Foot short, with slight anterolateral points. Body is translucent white.
Habitat:
Lives from low intertidal levels in rock pools to 90 m deep. They commonly associate with oysters but also with other bivalves.
Distribution:
Occurs from the Mediterranean to northern Norway (Distr. C. interstincta).