Order

Arcida

  Class

Bivalvia

  No. of Genera in Ref.

  No. of Species in Ref.

  Environment

Fresh : No | Brackish : No | Marine : No

  Aquarium

  First Fossil Record

     

  Remark

Shell equivalve, closed, solid, subequilateral, rounded more or less circular to oval-subquadrate in outline; anterior side usually more evenly rounded than posterior one which is often somewhat narrowed and angulated. Submedian orthogyrate, slightly prosogyrate or opisthogyrate umbones situated on top of a well-defined trigonal cardinal area which is deeply engraved by oblique or tent-shaped grooves and covered with a dark brown external ligament. External surface quite smooth, only striated radially and concentrically, or with radial ribs. Periostracum thick and densely set with fine hair, or thin to almost absent. Hinge plate broad and strongly arched, bearing a series of teeth diverging outwards which diminish in size medially and distally along the anterodorsal and posterodorsal margins. Internal surface porcelaneous. Two subequal adductor muscle scars, their inner margin with a radial ridge always stronger at front of the posterior scar. Pallial line without a sinus. Shallow burrowers of soft bottoms often containing a corase fraction, slowly ploughing through the substrate with the anterior end foremost, and binding the sand with mucus from the foot. Filter-feeding species. Able to colonize habitats of low oxygen concentration thanks to the presence of the respiratory pigment haemoglobin in the blood. Locally exploited by coastal people in the Western Central Pacific area (Ref. 348).

  Etymology

  Division

  Reproductive guild

  Typical activity level

  Main Ref.

  Coordinator