Platydoris striata from the Seychelles

Dear Dave,
This is indeed a Platydoris, and from the brown lines on the mantle I would identify it as Platydoris striata. You will see on the brief Fact Sheet I note that there is a pair of species with brown lines on the mantle and a pair with small brown spots. Each pair has one species with large red patches and one without. The brown-lined pair consist of your species, P. striata, and a red-spotted species, P. cruenta. Dorgan et al (2002) consider P. striata to be just a colour form of P. cruenta which lacks red spots. Their argument for synonymising the two species consists of the one sentence:
"This colouration [of P. striata] matches that of specimens of P. cruenta lacking red blotches, and therefore these two names are regarded as synonyms"
which is what I would call a rather circular argument. It would have been useful if they gave some evidence of comparing the anatomy of the two 'colour forms'.  It is strange they merged this pair of species with so little effort and yet retained the pair with brown spots, P. scabra and P. formosa, with no mention of their colour similarities.

It may be that P. striata is a colour form of P. cruenta but I consider synonymising species to be a much more exhaustive job than naming new ones, so will wait until someone produces some evidence. Another possibility is that it is another species. In an earlier message from Erwin Koehler [#4562] of an animal from the Seychelles, I tentatively identify it as P. scabra because it lacks brown lines, but both it and your animal have white rhinophore sheaths, whereas in P. scabra, P. striata. P. formosa and P. cruenta have brown spots or lines as elsewhere on the mantle.

I don't suppose you have a photo of the underside?

• Dorgan, K.M., Valdes, A. & Gosliner, T.M. (2002) Phylogenetic systematics of the genus Platydoris (Mollusca, Nudibranchia, Dorididea) with descriptions of six new species. Zoologica Scripta, 31(3): 271-319.

Best wishes,
Bill Rudman