Umbraculum laying eggs in New South Wales

March 11, 2001
From: Peggy Cable


I was on a Coast Care rockplatform walk with a group of people at Shelley Beach, Central Coast, New South Wales in January 2001. We were lucky to find Umbraculum umbraculum sitting on it's eggs. One of the members of our group, Ross Willis, was able to take some photos. He wondered why it was called an 'umbrella shell' until this one started lifting its shell and indeed looked for all the world like an umbrella.

Sincerely
Peggy

cablesdb@tac.com.au

Cable, P., 2001 (Mar 11) Umbraculum laying eggs in New South Wales. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/3894

Dear Peggy,
Thanks for thinking of the Forum, and thanks to Ross for taking the photos. Tom Thompson (1970) reported some facts and figures about an egg mass produced by a 16cm long animal from N. Stradbroke Id, Queensland. The uncoiled ribbon was 100cm long and 22mm high. The number of egg capsules per cm was 46,000 and there were on average 37 eggs in each capsule. This gave a grand total of over 4.5 million eggs in the whole ribbon. Hartley (1964) also published an account of egglaying and early development.

It never ceases to amaze me that this species can be found from the intertidal to 274 meters deep. One advantage of photographing the animal out of water is that you can see parts of its anatomy which are normally hidden by the shell. In the upper photo the umbrella-like shell is lifted to expose the smooth pale coloured cavity which is usually filled with water and encloses the gill which lies along the right side of the body. In this photo the gill is still hidden beneath the shell. I have also included an enlarged version of this photo showing the head region and its anatomy in a separate message.

Thanks again for this interesting find,
Best wishes,
Bill Rudman

References:
• Hartley, T.W. (1964) Egg laying and early development of Umbraculum sinicum Gmelin. J. Mal. Soc. Aust., 8(15 December): 33-35.
• Thompson, T.E. (1970) Eastern Australian Pleurobranchomorpha (Gastropoda, Opisthobranchia). Journal of Zoology, London., 160: 173-198.

Rudman, W.B., 2001 (Mar 11). Comment on Umbraculum laying eggs in New South Wales by Peggy Cable. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/3894

Factsheet

Umbraculum umbraculum

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