Nembrotha rutilans, N. aurea & N. purpureolineata

March 4, 2008
From: Bill Rudman

This may be the only message;I post today as it has involved a lot of moving of messages on the Forum to meet some changes in nembrothid nomenclature.

In Pola, Cervera & Gosliner's new paper on Nembrotha spp they have addressed the confusion surrounding the identity of animals I have previously identified on the Forum as Nembrotha rutilans and Nembrotha purpureolineata. They consider N. rutilans to be a junior synonym of N. purpureolineata, which is a decision I agree with. N. rutilans was named by Pruvot-Fol (1931) on the basis of a colour painting published in 1893, from Queensland, eastern Australia [message #21418], and N. purpureolineata was based on a preserved animal from Western Australia for which we have minimal information on the colour pattern. I think we can be fairly confident that both names are based on the same species. The brown colour pattern ranges from animals with many brown longitudinal lines to others in which the lines are merged into a solid brown 'saddle'.

Previously I have followed Gosliner (1971 - Nudibranchs of Southern Africa) in identifying the relatively common brown-lined Nembrotha from the Indian Ocean as N. purpureolineata. However Pola et al (2008) recognise this as a distinct species which they have named Nembrotha aurea. It seems that the main colour difference between the two species is that N. aurea has two dorsal orange patches, one in front of the gills and one behind. It also appears to have more consistent yellow markings as well. However the main part of the colour pattern of both species is the dark brown which in both species can range from multiple longitudinal brown lines right through to a solid patch [see messages #15763 for variation in N. purpureolineata; #3551 for N. aurea]. I have tried to find some anatomical differences without success. The only difference mentioned by the authors is that the rhachidian tooth in N. purpureolineata is broader than in N. aurea, but I wonder if that is because the animals of N. aurea studied were much smaller? Certainly the shape of the rachidian teeth in both species is remarkably similar, with even the same individual differences in denticulation showing up in both species - compare their Fig 10F with 22B, and 10D with 22C].

I am happy to go along with the separation, and are grateful for the author's work in providing us with so much new information on the anatomy of these animals, but I suspect we are looking at a 'work in progress'. For example what is the relationship between these two species and N. lineolata? Is the animal in message #19337 really N. purpureolineata or is it perhaps N. lineolata? And are the animals in messages #4740, #19904, forms of N. lineolata or a link showing how the brown 'saddle' is formed in N. purpureolineata?

When Terry Gosliner sent a copy of this paper to me he finished the accompanying message with the word 'enjoy'. I can certainly say I have enjoyed reading and thinking about their conclusions. It will certainly make the job of anyone in future studying these animals a lot easier.

• Pola, M., Cervera, J.L. and Gosliner, T.M. 2008. Revision of the Indo-Pacific genus Nembrotha (Nudibranchia: Dorididae: Polyceridae), with description of two new species. Scientia Marina 72(1): 145-183.

Best wishes,
Bill Rudman

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