New records of the rare Chromodoris obsoleta

August 5, 2004
From: Bill Rudman

PHOTO: Original figure from Ruppell & Leuckart, 1830: Tab. 9, fig. 3.

Tony Reavill's photos [#12729] of Chromodoris obsoleta are an interesting addition to our knowledge of the species. Originally described from the Red Sea, there are few records of this species. The original account describes it as milky white, with an orange-brown reticulation on the mantle, and a band of orange at the mantle edge, and a submarginal band of blue-black. To that description we can ass that the rhinophores and gills are translucent brown with the edges of the leaflets outlined in opaque white. The mantle colours show through ventrally, and the foot is white. The original illustration available to me suggests a brownish background colour but this does not accord to the written text and is possibly an artistic error or a result of the deterioration of the colour plate in the 170 years since its printing.

Eliot (1911) describes the external colour and radular morphology of specimens from the Red Sea but misidentifies it as a possible form of Chromodoris reticulata Pease [see Rudman, 1973]. Gohar & Soliman (1967) describe the embryology and life history of a species they identify with C. obsoleta but from their color description of the living animal it would seem that their animal species was a species of Glossodoris and not C. obsoleta.

I know of two other records, one from Seghala Is, Red Sea, which Nathalie Yonow sent to me for identification (Yonow, 1989) and a specimen from Suakin, on the Sudanese Red Sea sent to me by Chris Todd, [see separate message #12737]. I have also included photos of its radula [#12734] to show that it is a species of Chromodoris.

References:
• Eliot, C.N.E. (1911) Chromodorids from the Red Sea, collected and figured by Mr. Cyril Crossland. Proceedings of the Zoological Society of London, 2: 1068-1072. (Pl.61)
• Gohar, H.A.F. & Soliman, G.N. (1967) The direct development of the nudibranch Casella obsoleta (Rupp. and Leuck.) (with remarks on the metamorphosis). Publications of the Marine Biological Station, Al-Ghardaqa, Egypt, 14: 149-166.
• Rudman, W.B. (1973) Chromodorid opisthobranch Mollusca from the Indo-West Pacific. Zoological Journal of the Linnean Society, 52(3): 175-199, 7figs, 2col.pl.
• Rüppell, E. & Leuckart, F.S. (1830 or 31) Neue wirbellose Thiere des Rothen Meeres. Atlas zu der Reise im nördlichen Afrika von Eduard Rüppell. Brunner, Frankfurt am Main. 23-50, pls 7-12 pages.
• Yonow, N .(1989) Red Sea Opisthobranchia 2: The family Chromodorididae (Mollusca, Nudibranchia). Fauna of Saudi Arabia 10: 290-309.

Bill Rudman

Rudman, W.B., 2004 (Aug 5) New records of the rare Chromodoris obsoleta. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/12733

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