Re: Elysia from Colombia

October 16, 2000
From: Kathe R. Jensen

Dear Bill & Phanor,

The other possible ID for this Elysia is E. patina Marcus, 1980, which almost certainly feeds on Udotea. There has been some controversies about distinguishing E. papillosa and E. patina, but I think that E. patina has a long renopericardial prominence with many pairs (>6) of branching dorsal vessels, whereas E. papillosa has a short renopericardial prominence with few (<=4 pairs) dorsal vessels. The radular teeth also differ in shape, but this is where I had a disagreement with Kerry Clark, because my old radular mounts (for light microscopy) of E. papillosa teeth showed straight blades with coarse denticles, whereas Kerry describes narrow, curved or hooked teeth in Bermudan specimens collected from Halimeda. This is also the shape that I found in E. patina from Florida. Plasticity in tooth shape has been described in other sacoglossans, so this may not be a good distinguishing character in this case.

The egg mass may or may not be of this Elysia species. As far as I remember, E. papillosa has eggs with white extra-zygotic yolk. I cannot remember if E. patina has extrazygotic yolk, but as it has planktotrophic development, I doubt it. The eggs look more like those of the Halimeda-feeding E. tuca Marcus & Marcus, 1967.

Greetings,
Kathe

jensen@ait.ac.th

Jensen, K.R., 2000 (Oct 16) Re: Elysia from Colombia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/3173

Thanks Kathe,
Not an easy job to identify some species of Elysia from photos, especially when their taxonomy is still in some doubt. One problem I have found with old light microscope radular preparations is that the refractive index of the mounting medium can have a considerable affect on how denticles appear to even the most diligent observer. Because of the way light is curved by the interface between different media, in this case the glass, the mounting medium and the radula 'tissue', once a denticle, or other structure, becomes very thin it begins to appear very coarse to the viewer because the interface appears to be the object. In fact at a certain stage fine denticles appear as very coarse denticles. Really the only way to determine whether denticles are fine or coarse is to start again with a scanning electron microscope.

Best wishes,
Bill Rudman.

Rudman, W.B., 2000 (Oct 16). Comment on Re: Elysia from Colombia by Kathe R. Jensen. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/3173

Factsheet

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