Egg-laying Cuthona sibogae from Port Stephens

August 6, 2008
From: Leanne & David Atkinson

Dear Bill,
We found these eggs on a colony of the orange hydroid Sertularella quadridens, which had lots of Cuthona sibogae in it. We have never seen another nudibranch in this hydroid and these look like nudibranch eggs. We know you can't make a positive identification unless you actually see them laying the eggs but it would seem that these may be their eggs. Their eggs aren't mentioned in the fact sheet and there doesn't seem to be any other messages re their eggs. Have Cuthona sibogae eggs been observed before? We'll keep trying to catch them in the act of laying.

Locality: Fly Point, Port Stephens - Great Lakes Marine Park, Port Stephens, 12 metres, New South Wales, Australia, Pacific, 24 May 2008, Scattered sponges, hydroids, ascidians and soft corals on a sandy bottom. Length: Approximately 30 mm. Photographer: Leanne & David Atkinson.

Best wishes,
Leanne & David Atkinson

Atkinson, L. & D., 2008 (Aug 6) Egg-laying Cuthona sibogae from Port Stephens. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Leanne & David,

Thanks for the photos of the egg masses. You are right to be cautious, but I tend to agree with your strong suspicions that these are the eggs of Cuthona sibogae. I added a close-uup alongside showing a section of the hydroiod to show the fully extended polyps on which this aeolid feeds. In this species the polyps each have their own case [theca] into which the polyp can withdraw. Some hydroids, like Tubularia and its relatives don't have such cases and are known as athecate hydroids. In identifying thecate hydroids, obvious characters such as whether the stalks branch or not, and the nature of the branching, are used, but also the arrangement of the individual theca - are they arrangement opposite each other along each branch, or are they arranged alternately etc, etc. That's why it is very difficult for an expert to identify hydroid species from photos, unless the close-ups show the  stalks and the thecae very clearly. Even with such photos, I am afraid hydroid specialists are not that common.

Best wishes,
Bill Rudman

Rudman, W.B., 2008 (Aug 6). Comment on Egg-laying Cuthona sibogae from Port Stephens by Leanne & David Atkinson. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Cuthona sibogae

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