Relevant Synonyms Modiola senhousia Benson in Cantor, 1842 Arcuatula cf. senhousia (Benson, 1842) Misidentification Modiola (Arcuatula) arcuatula (Hanley, 1844) Arcuatula arcuatula Oliver, 1992  photo: S. Gofas / Coll. Verlaque

SHORT DESCRIPTION Shell thin, equivalve, oval, elongate. Outline modioliform; umbones subterminal; ligament and dorsal margins not continuous, slightly angled; anterior end rounded. Sculpture of radiating lines posteriorly, becoming weaker towards the margin. Concentric lines only in middle. Several mild riblets at anterior, causing a crenulate anterior margin. Ventral margin slightly concave. No hinge teeth. Periostracum shiny. color : pale olive-green with irregular brownish-purple markings and with the posterior lines a pale yellow-brown. common size : 10-25 mm in length, up to 12 mm in width. DISTINGUISHING CHARACTERISTICS Distinguished from Xenostrobus securis by the greenish color of the outer periostracal layer, by the radiating reddish lines on the posterior area and by the dysodont dentition on the dorsal edge just posterior to the ligament of the shell. While Modiola arcuatula Hanley, 1844 is a different species with a very swollen umbonal area, we agee with Hoenselaar and Hoenselaar (1989) that M. arculatula sensu Barash and Danin (1971) and sensu Oliver (1992) is M. senhousia. BIOLOGY / ECOLOGY Short-lived animal that grows rapidly and experiences dramatic population fluctuations. Separate sexes. Spawning time varies within a limited spawning season. Eggs and larvae are planktonic for 45-55 days. Reaches up to 25 mm in a year, and displays similar life-history characteristics as in its native range. Suspension feeder. Byssus well developed, forming an attachment to the substratum. May build important colonies and produces dense mats. habitat : an opportunistic species, attached by byssus to hard or soft substrata; lives in sheltered areas such as lagoons or estuaries subtidally to 20 m.

1st Mediterranean record Israel, 1971 [1960]. DISTRIBUTION Worldwide: Western Pacific from Siberia to Singapore. Introduced to NW America in 1924 and to Australia in 1983. Suez Canal ([50] Hoenselaar and Dekker, 1998). Mediterranean: recorded first in 1960 as Modiola arcuatula from Tel Aviv, Israel (Barash and Danin, 1971); successively from Bardawil lagoon, Egypt (Barash and Danin, 1971a); France, Etang de Thau (Hoenselaar and Hoenselaar, 1989); Italy, Ravenna lagoon, Adriatic Sea (Lazzari and Rinaldi, 1994); Slovenia (De Min and Vio, 1997). ESTABLISHMENT SUCCESS Well established in lagoons of the western Mediterranean, rare in the far eastern Mediterranean. speculated reasons for success : fouling organism, adaptated to a variety of habitats. Fits the classical concept of opportunist: a long planktonic dispersal stage, small, variable body size, high fecundity, short life-span. MODE OF INTRODUCTION Unknown. In French lagoons, populations have been probably imported with oysters for farming from Japan, around 1978. The Adriatic populations were possibly introduced with the clam Tapes philippinarum, imported for aquaculture in 1986. The Egyptian and Israeli records are accidentally transported from the Red Sea species locally called Arcuatula arcuatula. IMPORTANCE TO HUMANS May have an adverse impact on biodiversity as it reaches high densities that can exclude other infaunal species.

KEY REFERENCES Barash A. and Danin Z., 1971a. Mollusca from Sparus auratus. Argamon, 2: 97-104. Crooks J.A., 1996. The population ecology of an exotic mussel Musculista senhousia, in a southern California Bay. Estuaries, 19(1): 42-50. Hoenselaar H.J. and Hoenselaar J., 1989. Musculista senhousia (Benson in Cantor, 1842) in the western Mediterranean (Bivalvia, Mytilidae). Basteria, 53: 73-76.   Morton B., 1974. Some aspects on the biology, population dynamics and functional morphology of Musculista senhousia Benson (Bivalvia, Mytilidae). Pacific Science, 28: 19-33. FEEDBACK / COMMENTS TO AUTHORS

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