Okenia atkinsonorum - another pink species

December 10, 2007
From: Bill Rudman

Within a few days of publishing descriptions of two new pink species of Okenia, both of which feed on the bryozoan Pleurotoichus clathratus [see Rudman, 2004], I received a message to the Forum concerning a pink Okenia from the mouth of Botany Bay, Sydney [message #13723]. I automatically identified it as one of those new species, O. hallucigenia, which differed in colour and anatomy from the other, O. stellata . Some days later I began to have serious doubts about whether or not it was either of the new species, even though it was pink and like the other two fed on the same bryozoan.

One of the photos showed that the number of lateral processes was like neither species, so I asked the photographers to see if they could collect a few specimens. Despite their best efforts and the help of their dive club we did not find any specimens, but by then I had realised that all the other messages on the Forum which I had identified as O. hallucigenia were most probably this new species. Fortunately Leanne & David Atkinson were able to collect a few specimens for me from Port Stephens where there appears to be a permanent population. Sure enough, the internal anatomy, in particular the radula, shows that this is a third pink species living in eastern Australia and feeding on the bryozoan Pleurotoichus clathratus.

Locality: The Pipeline, west side of Nelson Bay, Port Stephens, New South Wales, Australia, on Pleurotoichus clathratus, 11 m, 11 June 2005, 13-15 mm long alive, AM C445669. Photos: Leanne & David Atkinson.

I have had great pleasure in naming it Okenia atkinsonorum in recognition of Leanne & David Atkinson's contributions to my research and their continuing contributions to the Forum. The description is published in Zootaxa. I have included here a few more of their photographs.

This week Ian Skipworth sent me more photos [message #21216 ] of the pink Okenia from northern New Zealand which I had previously suggested look similar to Okenia hiroi. In his latest photos it seems clear that it is most probably O. atkinsonorum as well, but as I have been mistaken before by photos of these pink species, I am now hesitant to be 100% sure without looking at the radula of this New Zealand animal.

• Rudman, W. B. (2004) Further species of the opisthobranch genus Okenia (Nudibranchia: Goniodorididae) from the Indo-West Pacific. Zootaxa, 695, 1-70.
• Rudman, W.B. (2007) Two new species of Okenia (Gastropoda: Nudibranchia: Goniodorididae) from eastern Australia and Tanzania. Zootaxa, 1657: 57–67.

Bill Rudman

Rudman, W.B., 2007 (Dec 10) Okenia atkinsonorum - another pink species. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/21273

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