(Linné, 1758)
Description (shell):
Shell depressed, elongate cap-shape; aperture applied to substratum, spire set posteriorly and to right; smooth, with irregular growth lines. Aperture elongate-oval, often slightly concave on spire side; edge thin, moulding to surface to which animal is attached; posteriorly a large shelf-like internal partition.
Size:
Up to 25 x 50 mm.
Colour:
Cream or pinkish, with streaks and blotches of reddish brown; throat chestnut-brown, with white partition.
Animal:
General organization like that of Calyptraea chinensis , but the mantle cavity much deeper and the gill longer; the penis is not bilobed. Colour is yellowish, with dark pigment on the snout, tentacles, mantle edge and penis.
Habitat:
On shells and stones on soft substrata; LWST to 10 m, often cast ashore by storms. The animals form curled stacks of up to 12 individuals; large shells at the bottom, becoming progressively smaller towards the apex of the chain. They are pests of oyster beds (C. fornicata).
Distribution:
An accidental introduction from America, it is now distributed from Essex along south coast to Bristol Channel, Belfast Lough, Co. Kerry, Helgoland and SW Netherlands (Distr. C. fornicata).