Relevant Synonyms Oscanius semperi Vayssière, 1897 Pleurobranchus perrieri Vayssière, 1897 Misidentification -  drawing: Tuvia Kurz

SHORT DESCRIPTION Large side-gilled sea slug, oval in outline. Mantle tough and tuberculate, covering entirely the broad foot, except for the tail that may just appear posteriorly in active animals. Anterior margin of the mantle deeply cleft. Rhinophores curled up to form a tube, united at their bases, with a broad oral veil beneath them. An elongated plume-like gill on the right side, between the mantle and the foot. Gill rachis with an alternating double row of tubercles. In adult animals no trace of any internal shell can be found. color : body color very variable, from peach or purple to dark brown or almost black. Opaque white or black circles or polygons frequently present on the dorsal surface (Gosliner et al., 1996). Foot of similar color, but slightly lighter. common size : up to 20 cm in length. DISTINGUISHING CHARACTERISTICS There are two species of the genus Pleurobranchus in the Mediterranean Sea: P. membranaceus (Montagu, 1803) and P. testudinarius Cantraine, 1840. The first clearly differs from P. forskalii by its smaller size, by lacking the characteristic network of opaque white or black lines, and by its very well-developed foot, by means of which it may swim. P. testudinarius is quite similar to P. forskalii at first glance, but it is more rounded in outline, the polygonal lines of the notum are violet and surround prominent swells. BIOLOGY / ECOLOGY Nocturnal; feeds on compound ascidians (Marshall and Willan, 1999). Its egg masses consist of a white spirally-arranged ribbon with one edge attached to the substratum and the other very wavy. habitat : it can be frequently observed crawling over sand and rubble bottoms (Gosliner et al., 1996). The Mediterranean specimens were dredged in sandy mud 48 m deep (Barash and Danin, 1977a).

1st Mediterranean record Israel, 1977 [1975]. DISTRIBUTION Worldwide: widespread in the Tropical Indo-Pacific, originally described from the Red Sea. Mediterranean: a single record in 1975 from Haifa Bay, Israel (Barash and Danin, 1977a). ESTABLISHMENT SUCCESS Only two specimens found in Israel many years ago. speculated reasons for success : - MODE OF INTRODUCTION Possibly via the Suez Canal. IMPORTANCE TO HUMANS None.

KEY REFERENCES Barash A. and Danin Z., 1977a. Additions to the knowledge of Indo-Pacific Mollusca in the Mediterranean. Conchiglie, 13(5-6): 85-116. Heller J. and Thompson T.E., 1983. Opisthobranch molluscs of the Sudanese Red Sea. Zoological Journal of the Linnean Society, 78: 317-348. Rudman W.B., 1993. Case 2838. Pleurobranchus forskalii Rüppell & Leuckart (1828) and P. testudinarius Cantraine, 1835 (Mollusca, Gastropoda): proposed conservation of the specific names. Bulletin of Zoological Nomenclature, 50(1): 16-19.   Thompson T.E., 1970. Eastern Australian Pleurobranchomorpha (Gastropoda, Opisthobranchia). Journal of Zoology, London, 60: 173-198. FEEDBACK / COMMENTS TO AUTHORS

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