Okenia atkinsonorum? from New Zealand

Dear Ian,

Thanks very much for these excellent photos. As luck would have it they arrived just after the final proofs of a paper describing a new species from eastern Australia - Okenia atkinsonorum - were returned to the publisher. I am pretty sure your animal is the same species, but because we now have 3 pink species in eastern Australia which are quite difficult to tell apart in photos, I would like to see the anatomy of your animal before I can be 100% positive - but on external shape and colour I can see no differences.

When you sent me photos before [messages #12958, #13019 ] I realised it was neither O. hallucigenia nor O. stellata but did not realise we had a third pink species in New South Wales at that time. At the time, I checked with Dennis Gordon, a bryozoan expert, who identified the pink bryozoan your animals were on to be a eurystomellid, which is the family of bryozoans that the Japanese O. hiroi and the Californian O. rosacea feed on, rather than the euthyrisellids that the eastern Australian ones eat. From the bryozoan identification and general shape, your earlier photos suggested a similarity to O. hiroi. Assuming your present photos are of the same species as your earlier ones, they show the same number and arrangement of dorsal papillae as O. atkinsonorum and as in that species, some of the papillae have rounded tips and others have pointed tips.

The only puzzle, is that in eastern Australia O. atkinsonorum feeds on Pleurotoichus clathratus [Euthyrisellidae] while your animal, from your earlier photos, feeds on a eurystomellid. Of course its possible that one species can feed on bryozoans from more than one family, but it has not been recorded before for any other of these pink species.

I checked the identity of the reddish bryozoan in your present photos with Dennis Gordon and he doesn't think it's either a eurystomellid or a euthyrisellid. As you mentioned that the slug was crawling along quite quickly it is probably just a coincidence it was passing a red bryozoan when you took your photos. Thanks again for sending in the photos, I am going to identify it as O. atkinsonorum, with the slight hesitation I have discussed above.

Best wishes,
Bill Rudman