Biogeographical homogeneity in the eastern Mediterranean Sea - I: the opisthobranchs (Mollusca: Gastropoda) from Lebanon

A review of opisthobranch species from Lebanon (eastern Mediterranean Sea), based on literature records (scattered throughout various papers published over a period of more than 150 years) and recently collected material (1999-2002 within the CEDRE framework and other samples), is presented, yielding a total number of 35 taxa identified to species level. Special emphasis has been placed on alien species, for which scattered notes are also given. The known opisthobranch biota is composed of 22 native (similar to 63%), 12 alien (similar to 34%) and one cryptogenic (similar to 3%) taxa. Eleven of these (Berthella aurantiaca, Berthella ocellata, Aplysia fasciata, Felimare picta, Felimida britoi, Felimida luteorosea, Felimida purpurea, Phyllidia flava, Dendrodoris grandiflora, Dendrodoris limbata and Aeolidiella alder) constitute new records for the Lebanese fauna, whilst the examined material of a further seven species (Elysia grandifolia, Pleurobranchus forskalii, Aplysia dactylomela, Bursatella leachii, Syphonota geographica, Goniobranchus annulatus, Flabellina rubrolineata), anecdotally cited from Lebanon on the basis of the samples studied here, is explained for the first time. One additional taxon belonging to the genus Haminoea has been identified to genus level only.