Crepidula fornicata

(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.

Up to 25 x 50 mm.

Cream or pinkish, with streaks and blotches of reddish brown; throat chestnut-brown, with white partition.

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.

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).

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).