Okenia rhinorma from S.E. Australia

Dear John,

Thanks for this interesting record. It is indeed O. rhinorma. It is amazing to think that until a couple of years ago the only examples of this species we knew about was a specimen I found in Dar es Salaam, Tanzania and a photo from the Red Sea. We now have records from the Indian Ocean across to tropical Japan and Australia. I must say I wasn't expecting it to occur in temperate Australia. I don't know if its appearance in Port Phillip Bay is the result of larvae travelling in ballast water or from global warming, or whether it is a 'natural' but irregular visitor.

The apparent burrowing behaviour is unusual but it could be a result of being in an unnatural environment. I suspect the sand is much looser than where you found it in the field, and it has sunk down into the sand until it has found the hard glass bottom. This species is very similar in shape to a few northern hemisphere species such as O. aspersa, O. leachi, O. ascidicola, O. elegans and O. pulchella. They are all relatively large with a high profile and all seem to feed on ascidians. Your other two messages showing the shape of the egg ribbon and it feeding on large solitary ascidians are both new observations for the species. These features confirm its link to the similarly-shaped species listed above.

Best wishes,
Bill Rudman