(Linné, 1758)
Description (shell):
Shell thin, more or less oval. Inequivalve: right valve with a distinct, rounded byssal notch in anterior ear, with fine teeth on lower border. Inequilateral: both valves with anterior ear more pronounced, twice as long as posterior. Sculpture of 25-35 bold ribs, and a few corrugated concentric lines, raised into prominent spatulate spines along ribs, most pronounced close to margin. Ears similarly ribbed. Growth stages usually clear (C. varia-drawing 2). Sculpture visible on inner surface, margin crenulate .
Size:
Up to 60 mm long.
Colour:
Colour very variable, from off-white, through yellow and orange to brick-red, purple, or brown, often with bands or patches of darker or lighter colour. Very young stages usually unicolorous. Inner surface of shell glossy, often coloured same as exterior (C. varia-drawing).
Animal:
Attached by byssus when young, but may become free later. Mantle with a double margin, the inner finely fringed and the outer edged with long tentacles. About 30 eye-spots at the base of the tentacles.
Habitat:
From lower shore to about 100 m. Often grows enclosed by algal holdfasts.
Distribution:
Widespread and common in the North Sea (Distr. C. varia). Present in the Mediterranean, distributed south to west Africa.