Order

Myida

  Class

Bivalvia

  No. of Genera in Ref.

  No. of Species in Ref.

  Environment

Fresh : No | Brackish : No | Marine : Yes

  Aquarium

  First Fossil Record

     

  Remark

Shell equivalve, globular to elongated, generally gaping anteriorly and posteriorly, although anterior gape is sometimes closed by a calcareous "calcium" in the adult shell. Dorsal margin unrolled over the umbones, forming an umbonal reflection. Anterior part of the valves with concentric and radial ribs, more or less spinose where they cross. A number of accessory calcareous plates about the main shell, along the dorsal margin and sometimes over the anteroventral gape and along the posteroventral margin. Periostracum thin, often more or less developed beyond shell margins. Ligament reduced, always internal. Hinge without teeth. Umbonal cavity often with a finger-like apophysis to which the foot muscles are attached. Three adductor muscle scars. Anterior adductor scar extending over the the umbonal reflection. Pallial line deeply sinuated, with the scar of the third adductor muscle ventrally. Gills elongate of eulamellibranchiate type, with 1 or 2 branchial sheets. Siphons long and united, smooth or papillate, often enclosed within a chitinous sheath. Foot more or less circular, truncated and forming a sort of sucker, atrophying in adult of species which develop a callum. Mantle fused ventrally, except at the pedal, anterior gape. The Pholadidae are highly specialized bivalves adapted for boring into relatively hard substrates such as limestone, sandstone, stiff clay or wood. Filter-feeding animals. Sexes separate, or alternating hermaphrodites (Martesia). Some Pholadidae are known for causing severe damage to rocky or wooden structures in harbours and other coastal areas. A number of species are collected for food (one is of commercial imporatnce in the Philippines), and are often considered a delicacy (Ref. 348).

  Etymology

  Division

  Reproductive guild

  Typical activity level

  Main Ref.

  Coordinator