Shell elongate-oval, umbones anterior to midline. Anterior hinge line sloping gently, continuous with convex anterior margin; posteriorly almost straight, forming an abrupt junction with the truncate, oblique, posterior margin. Valves with a distinct posterior gape. Sculpture of numerous fine concentric lines, forming low ridges anteriorly and posteriorly; fine radiating striations may also be present. Growth stages clear. Right valve with two bifid teeth, anterior broader than posterior; left valve with a bifid anterior cardinal and thin posterior cardinal. Adductor scars and pallial line distinct, cruciform muscle scars unclear. Pallial sinus deep, U-shaped, its lower edge largely fused with the pallial line (G. depressa).
Up to 60 mm long.
Glossy white, cream, or yellow, often with radiating streaks of reddish brown or lilac. Periostracum light or dark brown, thick and prominent around margins. Inner surfaces glossy, white, or yellowish, often tinted purple or blue, with external rays showing through.
The animal is yellowish white. Burrows with the broad thick foot usually extended as well as the long and sepatate siphons. Mantle edge is fringed.
In sandy substrata, from the lower shore into the shallow sublittoral.
Most frequent on southern and western coasts, ranging south to the Mediterranean and West Africa (Distr. G. depressa).