Ceratosoma amoena 'doing things'

April 27, 2007
From: Samuel Kemp

Dear Bill
Here are some 'activity' photos of Ceratosoma amoena for you. What causes the bumps on the surface of these slugs - surely not the cold? In the upper photo, the 2 slugs appear to have devoured most of the sponge on which they are enjoying themselves.

Locality: Poor Knights and White Island, 5-25 m, New Zealand, Pacific Ocean, Jan-Feb 2007. Photo: Samuel Kemp.

Samuel Kemp

samuel_kemp@hotmail.com

Kemp, S.V., 2007 (Apr 27) Ceratosoma amoena 'doing things'. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/19420

Thanks Sam,

Photos showing mating, egg laying and feeding in one message - it must be my lucky day! I have also added a close-up of your feeding photo alongside. In that photo, all that remains of the sponge they are eating is the network of fibres which form the skeleton in the group of sponges. As these sponges lack the mineral spicules found in the skeleton of most sponges, sponge taxonomists use the way these fibrous bundles are arranged to classify the families. Hopefully the arrangement is clear enough in your photos for me to get this sponge identified.

Concerning the bumps on the skin. A number of chromodorid species show this phenomenon to various degrees. Chromodorids, as well as having large mantle glands also have small glands scattered over the surface of the skin, and I think that's what these bumps are. As these animals have a fluid skeleton - they are a bit like a balloon filled with water - the skin in any one part of the body can vary in how stretched it is depending on what is happening elsewhere in the body. For example, during mating the mating apparatus has to be pushed out, and during feeding the oral tube is also pushed out so the fluid pressure in one part of the body can be lowered to allow for higher pressure elsewhere. At such times, the small glands are the only parts of the skin that can't change shape, so they stick out as small bumps.

Best wishes,
Bill Rudman

Rudman, W.B., 2007 (Apr 27). Comment on Ceratosoma amoena 'doing things' by Samuel Kemp. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/19420

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