Relevant Synonyms - Misidentification ? Mactra olorina  drawing: Tuvia Kurz

SHORT DESCRIPTION Shell equivalve, almost equilateral, inflated with a slight gape posteriorly. Outline oval; anterior margin roundish, posterior dorsal slope convex. Sculpture of irregularly spaced dense concentric ridges and lines, more pronounced at the anterior part of the shell, less prominent towards the posterior half. Pallial sinus small, oval. Margin smooth. color : variable; externally from white to purple-buff either uniform or with radial rays. Umbones always purple. Internally white to deep purple. common size : 30-40 mm width, 23-29 height; to 65 mm in the Eastern Arabia Sea (Bosch et al., 1995). DISTINGUISHING CHARACTERISTICS Very similar to Mactra olorina another Erythraean invader from which it differs by the color (see remarks under Mactra olorina) and in the concentric ridges: irregularly spaced in M. lilacea, evenly spaced ridges in M. olorina. BIOLOGY / ECOLOGY See notes on the biology of family under Mactra olorina. habitat : littoral to sublittoral sands; the Mediterranean record on the beach of Bardawil lagoon and also from depths 6-9 m along the Israel coast.

1st Mediterranean record Egypt, 2000 [1972]. DISTRIBUTION Worldwide: Indo-Pacific, Red Sea, including the gulfs of Aqaba and Suez, but absent from the Suez Canal. Mediterranean: recorded first in 1972, in Bardawil, Egypt (Mienis, 2000c); recently from Israel coast (Mienis, 2002b). ESTABLISHMENT SUCCESS Rare. The first Mediterranean record was based on a single valve and one complete specimen collected in the early 70's. However, the species has been recently encountered on the Israeli coast: alive in the Bay of Haifa (July 2001 Edna Scheffer, pers. comm.), also as empty shells on a beach some 100 km to the south (February 2002) (Mienis, 2002b). It is assumed that its resemblance to its congeneric M. olorina, a well-established Erythraean invader may have led to misidentifications. Collectors of molluscs are therefore urged to check their Mactra specimens. It may turn out that we are dealing with another well established Erythraean invader. speculated reasons for success : - MODE OF INTRODUCTION Possibly via the Suez Canal. IMPORTANCE TO HUMANS None.

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. Dekker H. and Orlin Z., 2000. Check list of Red Sea Mollusca. Spirula, 47(suppl.): 1-46. Mienis H.K., 2000c. First records of Mactra lilacea Lamarck, 1818 from the Eastern Mediterranean. Triton, 2: 16.   Mienis H.K., 2002b. Mariene Mollusken uit het Oostelijk deel van de Middellandse Zee. Een tweede vondst van Mactra lilacea. Spirula - Correspondentieblad van de Nederlandse Malacologische Vereniging, 325: 22. FEEDBACK / COMMENTS TO AUTHORS

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