Thorunna cf. florens from South Australia

Dear Stuart,
Welcome to the Sea Slug Forum. I am afraid I can't give you a definite answer on this one. I would need to look at the animal's anatomy to be sure. I am pretty sure it is what I have been considering to be a southern Australian variation of Thorunna florens, which was originally described from Japan. However as you can see on this page we are building up a collection of animals now with slightly different colour patterns. Whether they are all the same species will require a more detailed study of their anatomy.

I at first thought your animal was a colour form of another southern Australian species, Digidentis perplexa. It looks a bit different from the photos I have of that species on the Forum but it does look almost identical to an animal I have dissected from Port Philip Bay, Victoria, which has an anatomy identical to more 'typical' animals of Digidentis perplexa. However the orange patch on the front of the mantle in your photo is fairly characteristic of Thorunna florens and it does not occur in D. perplexa.
Another difference is that the mantle glands in D. perplexa are usually visible, crowded around the edge of the mantle. In your photo they are not prominent, which is typical of T. florens.

Whatever the species is, it would be good to see more photos from southern Australia of animals with similar colour patterns, because it is possible that there is an unrecognised group of similarly coloured orange-spotted chromodorid species in southern and south-western Australia to match the Red-spotted Group in southeastern waters.

Best wishes,
Bill Rudman.