Re: Thorunna cf. florens from South Australia

Dear Stuart,
I guess you are referring to Willan & Coleman, 1984. The photo there is definitely of Digidentis perplexa although it is of a much whiter animal than the normal translucent colour usually found in that species. I have dissected an identically coloured specimen and can find no anatomical differences.

Your animal is certainly similarly coloured, but I don't think it is the same. As I said in my earlier
comments, the mantle edge in your animal forms a wide flap and shows no sign of mantle glands, whereas in the Willan & Coleman photo, the mantle edge is very narrow and there are signs of a thick band of glands around the edge, which is typical of D. perplexa.

That is not to say that I definitely think your animal is Thorunna florens. At the moment that page has a collection of 'species', 'colour forms', call them what you may, which I think from experience are probably related. However until we get some anatomical information it is only a guess. Apart from the absence? or paucity of mantle glands, the orange mark at the anterior end of the mantle is beginning to look like a feature found in a number of species of Thorunna, including Thorunna montrouzieri, Thorunna sp. 1., Thorunna speciosus, as well as Thorunna florens.

The Thorunna florens page is a good example of taxonomic research 'in progress'. There is definitely no final word and until more material is available there is no prospect of resolving the question. However it is much better to leave it as a 'problem' than to rush out and name every colour 'form' as a new species.

As I also mentioned earlier, some groups of chromodorid nudibranchs show a remarkable ability to evolve almost identical colour patterns.

Best wishes,
Bill Rudman.