Ducal Thorny Oyster

Found attached to dead corals and rocks, in sheltered, shallow locations, of coral and rocky reefs.

Most Bivalves are permanently anchored in fissures or depressions in the rock surface of the reef, some may become covered in algae and other marine life.
Other Bivalves swim free, either by a well developed foot or propelled along by a jet of water from their mantle cavity.