Pholadomyoida

The Pholadomyoida are a diverse order of bivalve mollusks, characterized by their varied shell forms and often extensive mantle fusions. While generally equivalve, their shells can exhibit widely divergent shapes and are composed of aragonitic prisms and nacre, or homogeneous structures.1

Within this order, ctenidia are typically eulamellibranch and plicate, though many deepwater species possess septibranch ctenidia. They have reduced feet and pedal gapes, with siphons of variable length. Shallow-water Pholadomyoida are often burrowing, nestling, epibyssate, or cemented suspension feeders. In contrast, some deepwater species have evolved into predators with unique modifications to the typical bivalve plan. The family Pholadidae, which includes piddocks and related borers, belongs to this order.12