Shell small, thin but solid, equivalve, slightly inequilateral; dorsal anterior part inflated; posterior part rather obliquely expanded. Outline ovate when adult slightly higher than long, slightly truncated on the posterior. Sculpture of 49 rib (34-68 depending on area and population); interstices flat, as wide as the ribs or a little wider. Ribs weakly marked (flat or slightly rounded), more pronounced on posterior slope where they become irregular and the interstices become very wide. Intersticial riblets often present in posterior part more or less well developed. Periostracal insertions always on the posterior edge of the ribs.
very variable; externally from white to dark brown purple. Juveniles usually more colored than adults. Internally white to yellow or light pink.
common size :
to 35 mm in height.
The asymmetric hinge line forming a vague angle like a hump is diagnostic. Differences from F. fragilis in size, number and shape of ribs and outline are given under F. fragilis.
BIOLOGY / ECOLOGY
Unknown for the species. Generally cockles possess short siphons and are restricted to a shallow waters where they burrow in soft substrata. The genus is known as actively mobile, suspension feeder (Todd, 2002).
littoral to shallow water but also dredged from deeper waters 31-73 m in unknown substratum (Barash and Danin, 1992). Seems to prefer clean reefal or perireefal facies (Vidal, 1994).