Umbraculum laying eggs

April 10, 2003
From: Leanne & David Atkinson

Dear Bill,
We just read the message by Dee Scarr re the Umbraculum mating. Umbraculum are quite common at Port Stephens. We often see them on large orange barrel sponges where they are well camouflaged. We managed to catch one laying eggs and thought you might like to add it to the site. We've also included a "face" shot. The egg layers details are as follows:

Location: Fly Point, Marine Reserve, Port Stephens, NSW, Australia.
Date: 22 September 2001. Time: 12:16pm
Tide: High 1.6m Water Temp.: 18 degrees C.
Depth: 12m

Leanne & David Atkinson


Dear Leanne & David,
Thanks for filling another gap. In fact in your close-up alongside I can see a very interesting thing. If you look carefully at where the egg ribbon is emerging you can see it is coming out of a flap of tissue which has previously been identified as a permanent external penis. [see earlier photos]. It looks here as though this structure may be related to similar flaps of tissue found at the genital opening of the pleurobranchids, rather than being a penis. I'm afraid some anatomical structures are very difficult to interpret in preserved, often distorted animals. In the case of Umbraculum the structures at the front of the body lie in a groove in the extremely muscular body wall. When tha animal is preserved, the muscles of the body wall contract - even if the animal is 'put to sleep' first - so it is almost impossible to see this region clearly. All we need now is someone - an intrepid naturalist/diver - to gently pull two mating animals apart to see just what goes where during mating.
Best wishes,
Bill Rudman

Rudman, W.B., 2003 (Apr 10). Comment on Umbraculum laying eggs by Leanne & David Atkinson. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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