Identification key end: Gastropods: Crepidula fornicata

Crepidula fornicata usually sit in stacks on a hard substrate, e.g., a shell of other molluscs, boulders or rocky outcroppings. Up to 13 animals have been reported in one stack, but usually 4-6 animals are seen in a stack. Individual shells are up to about 60 mm in length, cap-shaped, distinctly longer than wide. The "spire" is almost invisible, slightly skewed to the right posterior end of the shell. Shell height is highly variable. Inside the body whorl is a characteristic calcareous shell-plate (septum) behind which the visceral mass is protected. There is no operculum. Shell colour is usually pale yellowish, often with an irregular pattern of reddish or brown spots or streaks. The high variability in shell coloration is reflected in the number of synonyms referring to appearance (maculata, violacea, roseae). Only other species of Crepidula are likely to be confused with this species. Recently another species has been found introduced in northern Spain (Collin et al., 2009), and it is possible that with increasing water temperature the species will disperse northwards. There are also two or three species that may be native to the Mediterranean, C. moulinsii Michaud, 1829, C. gibbosa Defrance, 1818 and C. unguiformis Lamarck, 1822 (WORMS). In addition C. aculeata (Gmelin, 1791) (=C. calyptraeiformis Deshayes, 1830) has been introduced into the Mediterranean from the Indo-Pacific (Ciesm, 200