Goniobranchus aureopurpureus

Order : NUDIBRANCHIA
Suborder: EUCTENIDIACEA
Infra order : DORIDACEA
Superfamily : DORIDOIDEA
Family : Chromodorididae

Goniobranchus aureopurpureus grows to about 40mm long. The mantle is white and there are yellow to dull brown irregular spots all over the central region. Right at the edge of the mantle is a band of diffuse watery purple and on its inside edge is a sub marginal band of large deep purple spots. In all specimens seen from Australia, there is a yellow spot or crescent on the inside edge of each purple spot. There is usually an unspotted zone, quite wide anteriorly, separating the sub marginal purple spots from the central region of the mantle spotted with yellow or brown.
The rhinophore clubs are heavily pigmented with purple or reddish brown and edged in white. The gills are translucent purple or red-brown, and also edged with white. The underside of the mantle, the sides of the body, and the foot are white except for the edge of the mantle which can be deep purple. There is some colour variation, with the dorsal spots ranging in colour from yellow to dull brown, and in size, from quite large blotches to small spots.

Goniobranchus aureopurpureus was originally described from the coast of China as having a mantle covered with “small irregular blotches of bright yellow of a roundish or elliptical form. Mantle edged with faint violet and an irregular row of deep violet-shaded spots running all round upon the faint edging”. Also the rhinophores and gills are of a dark colouration and edged in white. Specimens from Japan and China lack the yellow crescent or mark on the inside edge of each purple spot, which is found in specimens from Australia and New Caledonia. The faint violet marginal band and submarginal band of purple spots distinguish this species from Goniobranchus rufomaculatus and Goniobranchus alius, in which the purple spots are right at the edge. Another similar species from the western Pacific is Goniobranchus collingwoodi, and from the Indian Ocean, Goniobranchus tennentanus.

— Note by Pr. Bill Rudman — Australian Museum of Science – www.seaslugforum.net

Concerning this white and yellow-spotted group of Goniobranchus almost certainly suggest that 4 species of Goniobranchus, G. aureopurpureus, G. alius, G. rufomaculatus and G. albopustulosa  are most probably colour forms of one species. This is an interesting example illustrating the problems facing taxonomists when they try to interpret old descriptions and the immense value in studying local faunas and local variation within a species in great detail. Many early descriptions give brief features of the external shape and colour, and sometimes a coloured illustration of varying quality. Sometimes the original specimens still exist in some museum, but they are usually of little value at the species’ level, and so we are left with trying to find little clues from the original descriptions. All forms have rhinophore clubs which are dark brown or purple with white edging, and gills, which are held in a goblet shaped cluster, have opaque white edging. What we clearly need to do is to build up more information on their biology, what their egg ribbons look like and what sponges do they feed on.