August 31, 2009
From: Leanne and David Atkinson
Concerning message #19734:
We are glad to see you are able to post messages again. Hope you get some technical support soon. We came across these nudibranchs we haven't seen before. The first thing we noticed were the little white egg spirals on an ascidian. We looked closer to see if we could find a nudibranch and found this pair of transparent nudibranchs with one of the spirals.Not sure if one of them is laying these eggs or merely moving over them. The closest we could find to it was Hallaxa michaeli. Are we correct in our identification? Thanks for your help.
Locality: Halifax Sponge Gardens, Port Stephens-Great Lakes Marine Park, Port Stephens, 15 metres, New South Wales, Australia, Pacific Ocean, 15 August 2009, Sandy bottom with scattered sponges, bryozoans, ascidians, soft corals and gorgonias. Length: 10 mm. Photographer: Leanne and David Atkinson.
Leanne & David Atkinson
Atkinson, L. & D., 2009 (Aug 31) Re: Hallaxa michaeli on food sponge. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22626
Dear Leanne and David,
Yes this is Hallaxa michaeli. One characteristic of species of Hallaxa (and Actinocyclus) is the shape of gill circlet which is arranged in a goblet-like shape. It is a fool-proof way of identifying the genus. The sponge your animals are on is almost certainly the sponge Halisarca laxus, which is the only known food of H. michaeli. If we add the translucent whitish body I'd say you have ticked all the external character boxes.
You don't however mention the presence of stalked ascidians or cunjevoi. The sponge is considered to be found only in association with these stalked ascidians, and consequently Hallaxa has also only been found in association with them. That is not to say the sponge has read the rulebook, so if there were no stalked ascidians or cunjevoi around it would be interesting to know.
Re: Hallaxa michaeli on food sponge
From: Leanne and David Atkinson, September 14, 2009
Hallaxa michaeli on food sponge
From: Nicholas Missenden, March 23, 2007
Re: Hallaxa michaeli - feeding record
From: Nicholas Missenden, July 26, 2006
Hallaxa michaeli - feeding record
From: Nicholas Missenden, July 24, 2006
Hallaxa michaeli - radula photos
From: Bill Rudman, July 24, 2006