Marine bivalve mollusc, with oval shell consisting of 2 convex valves, the lower valve a little flatter than the upper one. Ears markedly unequal in size. Main sculpture of each valve with 25 to 35 regular, prominent, rounded, radial ribs. Color: outside of shell extremely variable, whitish, yellow, orange, red, brown or purple, often with irregular paler patterns. Interior glossy, with similar coloration or white often tinged with brown or purple. Maximum length 10 cm.