Pholadidae

Pholadidae, the family of bivalved mollusca of which Pholas, or the Piddock, is the type. The shell is gaping, is composed of very hard material, and is armed with strong ribs and teeth on the external surface: by means of these it excavates a vertical burrow in chalk, mud, and other soft rocks. The animal makes a, series of half-turns in its burrow and thus wears away the matrix, the powder of which is washed out by a current of water. They are all marine shallow-water inhabitants, and range in time from the Lias onward.