Shell equivalve, generally higher than long, irregularly oval. Area of attachment variable. Sculpture of 6-16 strong, raised, principal radial ribs with dense strong, moderately appressed spines of various lengths. In adults the umbonal area is usually worn. Wide, smooth interspaces, with one or two secondary ribs, which bear smaller spines. Inner margin finely crenulate.
interstices dark brown with white ribs and spines. Internally blue-white with purple red margin. Hinge brown.
common size :
to 70 mm in height.
Mature specimens of S. spinosus differ from S. groschi in the number of principal ribs (6-16 versus 6-7 in the latter), the shape of spines (large flat appressed versus regular overlapping spatulate spines in the latter) and coloration (white spines in S. spinosus).
BIOLOGY / ECOLOGY
Valve flapping as a reaction to attacks by Muricid gastropods. This antipredatory behaviour is comparable to the swimming escape mechanism shown by living Pectinidae (Mienis, 1994).
attached to rocky sea beds at depths 2-40 m; forms dense and strong populations along with Chama pacifica; the surfaces of their shells providing strongholds for a diverse community of algae and invertebrates.