Re: Elysia serca

March 22, 2004
From: Kathe R. Jensen

Dear Bill, Marina, Skip, and others,

Now I have finally got around to answering the Elysia serca / catulus questions [#12446]. There was one of my old papers that I could not locate in all my old piles of reprints and it has been more than 20 years since I worked with these animals, so I have to refresh my memory.

Concerning the feeding of E. serca / catulus, Marina's photo of the animal on Halodule [#12446] illustrates very well the feeding track. Halodule has very small epidermal cells and much bigger mesophyll cells. E. serca penetrates right through the epidermal cells and sucks cytoplasm from the mesophyll cells (which have few chloroplasts - or none?). Also, they empty more than one epidermal cell for each tooth penetration - including some in front of the mouth. The dark purple/brownish track is the "emptied" cells (which must still contain some sort of chemical that change colour when the chloroplast containing cytoplasm has been removed).

The animals look pale/starving because they cannot retain chloroplasts. I think this is because seagrass chloroplasts are not as robust as those of "siphonalean" algae. In our chloroplast symbiosis survey paper we had to measure C-14 uptake per animal because there was so little chlorophyll in these animals that we could not measure on a chlorophyll basis. We also found high levels of "dark-fixation", and thus no net photosynthesis.

The teeth of E. serca/catulus are rather strange in having a very tall base. I think that this is because they need to penetrate more than one cell wall at a time on a flat substrate. They prefer Halophila because this seagrass has only two layers of cells, both containing chloroplasts. The pharynx is shaped similar to that of Elysiella pusilla with a very thick layer of muscles surrounding the ventral limb of the radula. This would give added force to the leading radular tooth.

Unfortunately my observations on all this are spread in several publications - some of this due to referees' comments, but some due to me only gradually figuring out the feeding mechanism.

Information is found in the following publications:
• Jensen, K.R. 1982. Occurrence of Elysia serca Marcus in Florida, with notes on the synonymy and biology of the species. Journal of Conchology, 31: 87-94
• Jensen, K.R. 1983. Factors affecting feeding selectivity in herbivorous Ascoglossa (Mollusca: Opisthobranchia). Journal of experimental and marine ecology, 66: 135-148.
• Jensen, K.R. 1983. Further notes on the ecology and systematics of Elysia serca Marcus (Opisthobranchia, Ascoglossa). J. Moll. Stud. Suppl. 12A: 69-72.
• Clark, K.B., Jensen, K.R. & Stirts, H.M. 1990. Survey for functional kleptoplasty among West Atlantic Ascoglossa (=Sacoglossa) (Mollusca: Opisthobranchia). The Veliger, 33: 339-345.

Best wishes,
Kathe

krjensen@zmuc.ku.dk

Jensen, K.R., 2004 (Mar 22) Re: Elysia serca. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/12486

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