Re: Feeding ecology of Volvatella

May 31, 2000
From: Kathe R. Jensen

Dear Edwin & Bill,

Concerning Edwin's inquiry I'll be happy to supply whatever info I can. Volvatella is one of the poorest studied sacoglossan genera as far as ecology and biology goes - because usually only 2-3 specimens are found at any one time. Now that you are so lucky as to have recurring recruitments in Guam, you should certainly take the opportunity. I will list some of my papers containing observations on feeding, spawning and copulation in some species of Volvatella. However, it would be very interesting to have some experimental data on these processes.

For reproduction and development, I don't think anything is known for V. pyriformis. So you could start with describing the shape of the egg masses, counting the number of eggs contained, measuring the diameters of uncleaved eggs and egg capsules (surrounding individual eggs), recording the time from deposition to hatching (and if possible of various developmental stages in between). It should also be possible to determine the type of development (planktotrophic, lecithotrophic or encapsulated). If your supply of animals is big enough, you could try to identify minimum size for spawning and total number of egg masses produced over the reproductive period.

For feeding ecology: You are probably aware that all shelled sacoglossans feed exclusively on species of Caulerpa, but whether there is any species specific preference has never been experimentally studied. I have a hunch that "green" species (i.e. with digestive gland tubules in the mantle fold) are more species specific in their diet choice than are the "white" species. But I have never been in a situation where I had enough animals to do the experiments. There have also been claims in the literature that Volvatella feeds preferentially on the rhizoids of Caulerpa. Again this has never been corroborated by experiments. It would also be interesting to see if there is a difference in feeding activity in the light and in the dark (i.e. a possible preference for actively photosynthesizing algae or parts of the alga).

For biochemistry: As far as I know, no species of Volvatella has been included in the studies of bioactive chemicals. If you do decide to study this, please look for both diet-derived and de novo synthesized substances. Most studies deal with only one of these types.

References:
• Jensen, K.R. 1997. Sacoglossa (Mollusca, Opisthobranchia) from the Darwin Harbour Area, Northern Territory, Australia. Pp. 163-186 in: The Marine Flora and Fauna of Darwin Harbour, Northern Australia.
• Jensen, K.R. 1997. Sacoglossa (Mollusca, Opisthobranchia) from the Houtman Abrolhos Islands and central Western Australia. Pp. 307-333 in: The Marine Flora and Fauna of the Houtman Abrolhos Islands, Western Australia, Vol. 2.

Good luck with your studies,
Kathe

jensen@ait.ac.th

Jensen, K.R., 2000 (May 31) Re: Feeding ecology of Volvatella. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/2476

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