Splanchnotrophus elysiae n. sp. (Copepoda; Splanchnotrophidae) found parasitizing in the sacoglossan opisthobranch Elysia australis (Quoy and Gaimard, 1832)

Abstract

A new species of parasitic copepod, Splanchnotrophus elysiae n. sp. is described from the sacoglossan opisthobranch Elysia australis (Quoy and Gaimard) from southern Western Australia. The female copepod is about 1 mm long and brightly orange in life. It has a heavily sclerotized abdomen, which penetrates the epidermis of the host, and which bears the paired egg sacs. The male copepod is about 0.5 mm long and not as strongly modified as the female. The occurrence of copepods endoparasitic in shell-less opisthobranchs has recently been reviewed (Jensen, 1987). Seven species of the genus Splanchnotrophus have been described previously (Monod and Dollfus, 1932; Jensen, 1987). Apart from S. sacculatus (O'Donoghue, 1924), which was described from Australia, these are all north-east Atlantic and Mediterranean species. Most of the records are from aeolid nudibranchs (Jensen, 1987). In connection with the International Workshop on the Marine Biology of the Albany Area, Western Australia, a number of Elysia australis (Quoy and Gaimard, 1832) were collected intertidally in Eagle Bay, Cape Naturaliste, Western Australia. Several of these had orange markings on the parapodia, which on closer examination turned out to be parasitic copepods. A few of these had a pair of external egg sacs protruding through the dorsal epidermis of the host. During examination of numerous specimens of E. australis in the collections of the Western Australian Museum, a few more specimens infected by these copepods were found. These have been included in the present study. The parasitic copepod from Elysia australis is here described as a new species of the genus Splanchnotrophus.