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

Abstract

Phyllidiopsis sinaiensis (Yonow, 1988), of which only one single preserved specimen had been known, was rediscovered in the northern Red Sea. The dorsal colour-pattern of living individuals is presented for the first time, and the anatomy of P. sinaiensis is described in detail. Major features of the holotype previously used to characterise the species are shown to be artifacts. Principal distinguishing characters of P. sinaiensis include the central tubercle ridge, large and multicompound, broad based, pink tubercles, bicoloured black and pink rhinophores, the very elongate muscular oesophageal segment, the distinct stomach and the extremely long, convoluted prostate that is bound together by connective tissue. In some specimens, the bases of the tubercles may fuse leading to a predominantely pink dorsum with only a few black lines. Phyllidiopsis sinaiensis appears to be among the most common nudibranchs in the Gulf of Aqaba. The fact that it has not been reported since its original collection in 1980 can be explained by being confused with the externally similar, well-known species Phyllidiella pustulosa (Cuvier, 1804). A review of the phyllidiid fauna of the Red Sea reveals eleven valid species that can all be identified with the key presented herein. With four out of eleven species, phyllidiid endemism (36%) is high in the Red Sea. This is in contrast to recent palaeobiological hypotheses of a post-glacial origin of the Red Sea coral reef fauna.