Shell equivalve, almost equilateral, inflated with a slight gape posteriorly. Outline oval-trigonal; anterior margin roundish, posterior rostrate. Sculpture of dense concentric striae, more pronounced at the anterior part of the shell, less prominent towards the posterior half. Lunule oblonge-oval, escutcheon present. Ligament internal on a chondrophore. Pallial sinus small, oval. Margin smooth.
externally whitish or beige often with dark rays. Escutcheon and lunule dark brown.
common size :
shell to 60 mm.
The oval-trigonal outline and the prominent anterior sculpture are diagnostic features of the species. However, in the Red Sea, small individuals can be confused with M. lilacea Lamarck, 1818. They can be distinguished by the color of the umbonal area; white in M. olorina, purple-brown in M. lilacea.
BIOLOGY / ECOLOGY
The Mactridae live buried in the sand or mud but often after sea storms, it is possible to find large heaps on the beaches even if only detached valves or dead shells. The movements responsible for recovery from deep burial were examined at a population in southwest India. It was observed that rapid burrowing and active upward movement through the sand, as appropriate, enable the animal to maintain its position in disturbed sediments (Ansell and Trevallion, 1969). Suspension feeders.
littoral and sublittoral sands.