June 10, 2001
From: Lindsay Warren
To accompany the photos and details of Dermatobranchus albus found by Jean Coop in the Tukang Besi Archipelago, SE Sulawesi [Operation Wallacea], here are details of some additional specimens I found during last year's survey season. OS01007 (bottom photos)was found at the end of August 2000 in the afternoon at a depth of 5ft, size: 16mm, while OS01080 (upper right) was found in mid October at a depth of 28 ft, size: 22mm.
In looking up references on known species I came across Eliot's original description of Dermatobranchus albus (Eliot, 1904):
"Back white with distinct low ridges, longitudinal but not parallel to median line, each with a yellow line along its summit. The rhinophores stand vertically or point forwards and bear longitudinal perfoliations. The base is white, the main part black, the apex truncated and yellow. They are not retractile into pockets, but can be withdrawn under the mantle-edge. They are not very sensitive. The large velum and the mantle are edged with bright yellow. Foot not half the width of mantle. In crawling, the underside of the mantle is applied to the substratum over which the animal moves. Length 13 mm, breadth 4 mm."
And a further description of the same species (Edmunds & Thompson, 1972):
"The two animals were 16 and 9 mm long alive and they crawled actively in captivity. Dorsally the mantle has a series of almost parallel longitudinal ridges and grooves. The ridges have a yellow crest with white sides, and the grooves are grey. The edge of the mantle is yellow. Between the rhinophores the mantle is continuous with the head, unlike Armina which has a ridge and a groove here. The oral veil is white with a broad yellow anterior border. The rhinophores are white at the base with a yellow club and tip, but the club has dense black spots so appears dark. There are about eight longitudinal ridges on the club. The foot is rounded anteriorly with angled corners. Preserved, it is rounded with rounded corners. On the ventral surface, both the mantle and the foot are white. As usual in this family, there are openings of glands all along the edge of the mantle on the ventral side, but there are no lateral lamellae or gills such as occur in Armina. The smaller animal has a similar pattern to the larger one except that many of the yellow ridges on the mantle are discontinuous."
These seem to fit the specimens we found quite well. Without looking at internal anatomy at this stage, and considering that this D. albus has been described from the Eastern Indian Ocean, do you think it would be reasonable to think that Dermatobranchus albus could be the right id for the specimens we have found? The only difficulty with the external details is that there is no note on Jean's illustration as to whether the ridges were capped in yellow or whether yellow appeared in the grooves between the ridges although in the case of OS01007 it certainly looks as if there is a thin yellow line on top of the ridges with white walls and 'dirty' yellow grooves. Sadly I didn't pay attention to this when we found the various specimens and I had not found the above descriptions of D. albus.
• Eliot, C.N.E., 1904. On some Nudibranchs from East Africa and Zanzibar. Part V. Proceedings of the Zoological Society of London, 2(1): 83-105.
• Edmunds, M. & Thompson, T.E., 1972. Opisthobranchiate mollusca from Tanzania IV. Pleurobranchomorpha, Dendronotoidea and Arminoidea. Proceedings of the Malacological Society of London, 40(3): 219-234, fig. 4.
Looking forward to your comments.
All the best
Lindsay Warren , 2001 (Jun 10) Dermatobranchus albus from SE Sulawesi . [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/4447
I have had a look at my field notes of specimens I collected in east Africa and at least externally your animals fit Eliot's D. albus. There is usually a thin yellow line along the centre of the longitudinal ridges but what gets confusing, especially in dorsal photos is separating the ridges from the 'grooves'. The 'grey' colour between the ridges reported by Edmunds is really a translucent region, sometimes a colourless 'grey' but in other specimens a yellowish colour.