Is Elysia viridis a single species?

August 9, 1999
From: Cynthia D. Trowbridge

Dear Bill,

I would be interested in hearing other people's views about cryptic species, their frequency in different orders of opisthobranchs, and what criteria should be used to determine whether taxa are different species vs. different forms, varieties, or races (i.e., exhibiting intraspecific variation). The issue becomes quite complex in taxa such as sacoglossans whose body size, body shape, color, and radular tooth attributes can all be influenced by diet.

In particular, I would also be curious if anyone thinks Elysia viridis in the NE Atlantic may not be a single species but rather two or more "cryptic species". I consider E. viridis to be a single good species but have been given the task of defending this on ecological, morphological, and genetic grounds. I am familiar with the work by Kathe Jensen, Michael Miller, and others on the species but would appreciate hearing about color, size, behavioral variation in E. viridis that may cause you to consider there are more than one species.

I look forward to discussing this issue with people. Please respond either to me directly or to the group. Thanks!!!

Cynthia D. Trowbridge
Research Assistant Professor
Hatfield Marine Science Center
Oregon State University, USA

trowbric@bcc.orst.edu

Trowbridge, C.D., 1999 (Aug 9) Is Elysia viridis a single species?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/1173

Dear Cynthia,
I guess by 'cryptic species' you don't mean a species showing cryptic colour patterns (ie: camouflage), but rather a group of species difficult to distinguish from each other because of their morphological similarities.

I would be very interested in some examples of the sacoglossans you refer to whose body size, body shape, color, and radular tooth attributes can all be influenced by diet.

It would also be very useful if you could provide us with some photos of the different 'morphs' of Elysia viridis and of any of the other species which are polymorphic or perhaps are cryptic species groups. I guess the problematic Placida dendritica, which is supposed to have a worldwide distribution, is another good example.

While many of these northern hemisphere species are very familiar to you, and have spawned a huge and interesting literature, we in the southern hemisphere, though familiar with the literature, are unfamilar with the animals. I am happy to post pictures of these 'species' from throughout their geographic ranges, if it helps in stimulating discussion.

Concerning people responding directly to Cynthia or the Forum. If you respond directly to Cynthia could you send a copy to the Forum? I would like the Forum to be used more for open discussion, and open discussion dies very quickly if all the replies bypass the Forum.

Thanks to Daniel Geiger for another very welcome photograph.

Best wishes,
Bill Rudman.

Rudman, W.B., 1999 (Aug 9). Comment on Is Elysia viridis a single species? by Cynthia D. Trowbridge. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/1173

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