Shell medium sized, slightly laterally compressed. Outline subovate distinctly longer than high with umbones towards the anterior part. Sculpture of nodulose radial ribs; asymmetrical ribs on the posterior slope where they change direction and are obliquely placed in relation to the central ribs; the divaricate ribs of the posterior slope are concentrically striae from the top to the bottom and concentric grooves continue into the symmetrical radial ribs near the ventral margin. Narrow heart-shaped lunule. No pallial sinus. Inner margin crenulate.
exteriorly white to cream occasionally spotted upon the radial ribs with brown, lunule stained with purple underneath the beaks. Internally white with a cream flush within the pallial line area, ligament stained with violet.
common size :
shell to 50 mm in length.
Similar in size and outline to G. tumidum but differs in the following features: the radial ribs are coarser and more frequently bifid towards the ventral margin; the granules upon the radial ribs are larger and more distant from each other; the concentric striae are more prominent (Cernohorsky, 1972).
BIOLOGY / ECOLOGY
It lives for up to 3 years with low levels of recruitment taking place in two phases, in spring and autumn. Gametogenic cycles confirm this picture. Matures at a shell length 16-20 mm, after one year of life. Generally it is a dioecious species with sex rato about 1:1.
intertidal and shallow water; muddy gravels and sands.