REDESCRIPTION OF PHYLLIDIOPSIS SINAIENSIS (YONOW, 1988) (NUDIBRANCHIA: DORIDOIDEA: PHYLLIDIIDAE), WITH A REVIEW OF THE RED SEA PHYLLIDIIDAE

Phyllidiopsis sinaiensis (Yonow, 1988), of which only one single preservedspecimen had been known, was rediscovered in the northern RedSea. The dorsal colour-pattern of living individuals is presented forthe first time, and the anatomy of P. sinaiensis is describedin detail. Major features of the holotype previously used tocharacterise the species are shown to be artifacts. Principaldistinguishing characters of P. sinaiensis include the centraltubercle ridge, large and multicompound, broad based, pink tubercles,bicoloured black and pink rhinophores, the very elongate muscularoesophageal segment, the distinct stomach and the extremelylong, convoluted prostate that is bound together by connectivetissue. In some specimens, the bases of the tubercles may fuseleading to a predominantely pink dorsum with only a few blacklines. Phyllidiopsis sinaiensis appears to be among the mostcommon nudibranchs in the Gulf of Aqaba. The fact that it has notbeen reported since its original collection in 1980 can be explainedby being confused with the externally similar, well-known speciesPhyllidiella pustulosa (Cuvier, 1804). A review of the phyllidiidfauna of the Red Sea reveals eleven valid species that can allbe identified with the key presented herein. With four out of elevenspecies, phyllidiid endemism (36%) is high in the Red Sea. This isin contrast to recent palaeobiological hypotheses of a post-glacial originof the Red Sea coral reef fauna.