Relevant Synonyms Mactra isthmia Jousseaume, 1888 Trigonella olorina (Philippi) [Cooke, 1886] Misidentification -  photo: W. Engl

SHORT DESCRIPTION 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. color : externally whitish or beige often with dark rays. Escutcheon and lunule dark brown. common size : shell to 60 mm. DISTINGUISHING CHARACTERISTICS 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. habitat : littoral and sublittoral sands.

1st Mediterranean record Port Said, Egypt, 1889 [no collecting date]. DISTRIBUTION Worldwide: endemic in Red Sea; recorded in the Suez Canal (Tillier and Bavay, 1905). Mediterranean: recorded first from Egypt, Port Said (Carus, 1889-93); successive reports from Lebanon (Gruvel and Moazzo, 1931); Israel (Barash and Danin, 1973). ESTABLISHMENT SUCCESS Well established in Bardawil lagoon (Egypt), moderately elsewhere. speculated reasons for success : the sandy and muddy grounds of the Bardawil lagoon provide suitable substrata for the shallow burrowing Mactra olorina. MODE OF INTRODUCTION Via the Suez Canal. IMPORTANCE TO HUMANS Edible but not of high economic interest. Locally common in Bardawil.

KEY REFERENCES Ansell A.D. and Trevallion A., 1969. Behavioural adaptations of intertidal molluscs from a tropical sandy beach. Journal of Experimental Marine Biology and Ecology, 4(1): 9-35. Barash A. and Danin Z., 1973. The Indo-Pacific species of mollusca in the Mediterranean and notes on a collection from the Suez canal. Israel Journal of Zoology, 21(3-4): 301-374. Carus J.V., 1889-1893. Prodromus Faunae mediterraneae sive descriptio animalium maris Mediterranei incolarum. Vol. 2: Brachiostomata. Mollusca. Tunicata. Vertebrata. IX + 854 p., E. Schweitzerbart, Stuttgart, [pp. 1-272 issued 1889] [Mactra olorina p. 143].   Gruvel A. and Moazzo G., 1931. Contribution à la faune malacologique marine des côtes Libano-Syriennes. Pp. 437-456. In: A. Gruvel (ed.), Les états de Syrie. Richesses marines et fluviales. Société des Editions Géographiques, Maritimes et Coloniales, Paris. Tillier L. and Bavay A., 1905. Les mollusques testacés du Canal de Suez. Bulletin de la Société Zoologique de France, 30: 170-181. FEEDBACK / COMMENTS TO AUTHORS

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