Shell is a short, broad cone with a blunt apex and a slightly cyrtoconoid spire. There are four nearly flatsided postlarval whorls with sutures lying nearly at right angles to the shell axis. The whorls of spire have numerous costae. There are about thirty costae on the adapical half of the last whorl, slightly prosocline and usually straight, and up to eight spiral ridges on the basal half ; the ridge nearest the periphery is the broadest. Though costae and spiral ridges do not cross the latter may be slightly tuberculated in line with the costae. Last whorl occupies about two thirds of the total height. Aperture has the shape of a rounded lozenge; it occupies about 45 % of the total height. Outer lip is prosocline in side view; it arises level with the topmost ridge and it is everted at base of columella. The inner lip everts over a marked umbilical groove. The tooth is visible (C. pellucida-drawing).
Up to 3 x 1.8 mm.
The body has short tentacles, rather narrow, with a slight bulge at the base of the lateral marginal groove. An eye lies level with this bulge in line with the median edge of each tentacle. The mentum is narrow, its tip often expanded. The foot is rather broad, slightly concave anteriorly with weak anterolateral corners. White or cream with opaque white flecks, a white line along each tentacle and a white spot at its tip.
The animals live from LWST to depths of about 120 m, commonly in association with colonies of Pomatoceros and Sabellaria , on which they feed.
This species ranges from the western Mediterranean to Norway and Denmark. It has been found alive, moderately frequently, on all coasts of the British Isles and Helgoland, though only dead shells occur in the eastern Channel (Distr. C. pellucida).