Solid shell up to 15cm in length. The valve is flat and red brown in colour. The right is convex and white or cream in colour. The inside of both valves is white. The surface is sculptured with prominent radiating ribs and finer concentric lines.
- Upper valve flat; lower one convex
- Both valves have 15 to 17 radiating ribs
Juveniles live attached by byssus threads but as the animal matures it becomes free living. It prefers bottoms of sand or gravel where it rests in a self made depression. It can swim when necessary particularly when threatened. It filter feeds phytoplankton from the water column.
CommonDistributed from northern Norway to the Iberian Peninsula