Goniobranchus geminus

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

DISTRIBUTION
Tropical Indian Ocean.

This is one of a group of similarly coloured species, the “Hypselodoris tryoni colour group”. Other species include Hypselodoris tryoni, Goniobranchus kuniei and Chromodoris leopardus. They all have large purple or purple-brown spots or marks, usually ringed with white, an often reticulate brownish background, and a purple border. Goniobranchus geminus differs in having four colour bands around the mantle edge, an outermost white, then translucent greyish purple, then white, then yellow. The other three have a distinct purple line at the border, narrow in Chromodoris leopardus and Hypselodoris tryoni, but broad in Gioniobranchus kuniei. The shape of the body of H. tryoni, high with a reduced mantle overlap is typical. The three species of Hypselodoris have a wide mantle overlap. Of the three with the purple mantle edge, C. leopardus and G. kuniei can be distinguished from H. tryoni by the broad purple border, consisting of three slightly different coloured bands in G. kuniei, and by the leopard-like multiple spots, or marks, forming a hollow square, found in C. leopardus.

See also the recently described Goniobranchus tritos, which may be a colour form of G. geminus and Goniobranchus cf. geminus which has recently been reported from South Africa and has a very similar colour pattern.