(Montagu, 1803)
Description (shell):
Shell triangular, its greatest dimension being along its dorsoventral axis; umbones prominent, situated on midline. Lunule and escutcheon indistinct, shallow. Sculpture of numerous fine concentric lines, closely spaced. Growth stages distinct. Right valve with two cardinal teeth, anterior broad and triangular, posterior slender. Left valve with two approximately equal-sized cardinals, posteriorly a third one appears as a ridged projection, like a lateral tooth. On inner surface a margin with distinct beadlike crenulations (G. triangularis-drawing).
Size:
Up to 3 mm long.
Colour:
Colour white, overlain by light yellowish to brown periostracum. Inner surface white.
Habitat:
Occurs offshore, to at least 100 m, in sand and fine gravel.
Distribution:
Distributed south to the Mediterranean and north-west Africa (Distr. G. triangularis).