Shell moderately convex, ovate, rather thin, with apex at posterior margin, slighly curled dextrally. Outer surface smooth or with only growth lines. Inside with a septum which occupies the posterior half. Edge of shell thin and cutting.
exterior with pale purplish or brownish stains on a dirty grey background; inside with a similar but vivid pattern of purplish blotches, and white septum.
common size :
up to 50 mm in the Atlantic, Mediterranean specimens smaller.
This species is distinguished from the native species by being definitely convex and growing much larger, and by the mottled color pattern; from the West African C. porcellana (Linnaeus, 1758) by its larger size and profile which is evenly rounded, not subcarinate.
BIOLOGY / ECOLOGY
Individuals of Crepidula fornicata pile up on each other, the older specimens being females and the younger (on top), males which will eventually turn into females as the pile grows. The biology of this species has been studied in detail by Le Gall (1980).
on sand or gravel bottoms in low energy environments, in which the accumulation of shells may lead to the formation of a biogenic hard substrate.