Relevant Synonyms Mytilus pharaonis (Fischer P., 1870) [Tillier and Bavay, 1905] Mytilus variabilis Krauss, 1848 Mytilus arabicus Jousseaume ms. in Lamy, 1919 Brachidontes semistriatus (Krauss, 1848) Brachidontes variabilis [many authors] Misidentification -  photo: S. Gofas / Coll. G. Bitar

SHORT DESCRIPTION Shell equivalve, inequilateral. Outline mussel-like with terminal umbones but variable in shape and in its height/length ratio; sometimes greatly expanded posteriorly, sometimes arcuate; occassionally subcylindrical with beaks not quite terminal. Sculpture of numerous fine radial bifurcating ribs, which become coarser posteriorly. Hinge with dysodont teeth. Margin crenulate. color : externally dark brown-black; internally tinged violet-black. common size : shell to 40 mm. DISTINGUISHING CHARACTERISTICS Resembles very much the Red Sea species Septifer bilocularis, from which it is distinguished by the absence of a septum beneath the beaks and by the darker color (the latter is bright green with reddish spots). BIOLOGY / ECOLOGY Typical inhabitant of hard substrata. Its abundance seems to be negatively associated with wave exposure. The animals colonize debris. Entangling the hard fragments by byssus threads into larger and heavier masses, they may reach very high densities and cover completely a rocky shore to form a "mytilid bed" (Safriel et al., 1980). Suspension feeders. habitat : lives in shallow water (at sea level or just below) attached by its byssus to rocks and stones, mostly in clusters.

1st Mediterranean record Egypt, 1878 [1876]. DISTRIBUTION Worldwide: Indian Ocean, Red Sea; recorded in the Suez Canal (Tillier and Bavay, 1905). Mediterranean: first record from Port Said, Egypt in 1876 (Fuchs, 1878); successively from Lebanon (Gruvel and Moazzo, 1931); Israel (Haas, 1937); Sicily (Di Geronimo, 1971); Greece, Chalkida, Evvoikos (Koroneos), 1979; Syria (Kinzelbach, 1985); southern Turkey (Kinzelbach, 1985); Greece, Rhodes (Tenekides, 1989); northern Cyprus (Cecalupo and Quadri, 1996); Croatia, northern Adriatic (De Min and Vio, 1997). ESTABLISHMENT SUCCESS One of the earliest recorded and most successful of the Lessepsian immigrants, which now constitutes large, stable populations. Locally invasive. Accidental records in the western Mediterranean cannot be evaluated. Recent finding in Croatia are likely due to ship transport linked with the oil terminal of Trieste. speculated reasons for success : favoured by debris. Open question: can it thrive in harbour environments with oil pollution and replace M. galloprovincialis (De Min and Vio, 1997)? MODE OF INTRODUCTION Via the Suez Canal. According to molecular studies, there are some Red Sea genotypes in the Mediterranean, but the non-Red Sea genotypes are fairly common and increases in frequency as one gets further away from the Suez Canal (Abelson, pers. comm.). This suggests ship transport as a major vector. IMPORTANCE TO HUMANS None.

KEY REFERENCES Fuchs Th., 1878. Die geologische Beschaffenheit der Landenge von Suez. Denkschriften der Kaiserkichen Akademie der Wissenschaften, Mathematisch-Naturwissenschaftliche Classe, 38: 25. Gruvel A. and Moazzo G., 1931. Contribution à la faune malacologique marine des côtes Libano-Syriennes. Pp. 437-456. In: Gruvel A. (ed.), Les états de Syrie. Richesses marines et fluviales. Société des Editions Géographiques, Maritimes et Coloniales, Paris. Kinzelbach R., 1985. Lesseps'sche Wanderung: neue stationen von Muscheln (Bivalvia: Anisomyaria). Archiv fur Molluskenkunde, 115(4-6): 273-278.   Pallary P., 1912. Catalogue des mollusques du littoral méditerranéen de l'Egypte. Mémoires de l'Institut d'Egypte, 7: 69-207, pl. 15-18. Safriel U.N, T. Felsenburg and A. Gilboa., 1980. The distribution of Brachidontes variabilis (Krauss) along the Red Sea coasts of Sinai. Argamon, 7(3): 31-43. FEEDBACK / COMMENTS TO AUTHORS

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