Solid wedge shpaed shell up to about 15cm in length (though exceptionally may be bigger). The outside is purple, blue or brown in colour; the inside is pearl white bordered with purple or blue. The surface is sculptured with concentric rings.
- The beaks are at the anterior end of the shell
Lives attached by byssus threads to any suitable hard substrate. It is very gregarious and often occurs in very dense beds. Even once anchored some movement is still possible by dropping some of the byssus threads. Feeds by filtering phytoplankton.
Distributed from Norway south to the Iberian Peninsula and into the Mediterranean.