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Pholadina (class Bivalvia, order Myoida) A suborder of thin-shelled, unequilateral bivalves, which differ from other members of the order in possessing one or more additional plates. The foot is circular and acts as a suction disc. A small internal ligament and chondrophore are present. There are no hinge teeth. Musculature is isomyarian. The gills are elongate, with a pair of demibranchs in most forms. Pholadina live in holes that they bore, commonly on a rock, coral, or wood substrate. They first appear in rocks of Jurassic age.