Re: What's wrong with Elysia clarki?

September 1, 2006
From: Skip Pierce

Concerning message #17670:

Hi Bill
The answer to your question is that, as you've answered it yourself, there is nothing wrong with E. clarki, especially if a comparison is made to the descriptions of several other elysiid species. I have not seen the book that you've reviewed, but from your comments, what is wrong here is the authors' opinion, which seems based on no new data, ignorance of the existing data and no research to support their opinion.

On the other hand, I think if you look at our paper describing E. clarki, you will find much more documentation, than regrettably, usually accompanies descriptions of elysiid species. Furthermore, our comparison of E. clarki with E. crispata covered many levels, from ecology, to feeding, to larval development, to symbiotic chloroplasts, to radular morphology, to digestive system morphology, to microscopic anatomy at both light and electron microscopic levels, to molecular biology - and the two species were consistently and, importantly, predictably different in EVERY characteristic in EVERY specimen - and we've looked at 1000s of specimens over many years - live and preserved. The differences hold up not only between E. crispata from the Virgin Islands and E. clarki, but also between E. crispata from Florida reefs and E. clarki, as well as among preserved specimens from a variety of locations - all of which we looked at. Not all are data is included in the published description because during a long and exhaustive gestation period, journal reviewers insisted, amongst other things, that the manuscript be shortened.

Some of the characters are subtle - but some, as you have mentioned, Bill -are major. In fact, the anterior gap vs fusion in the parapodia has been used by some authors as a genus-separating characteristic. According to some schemes, the fused parapodia suggest that E. crispata should not even be in Elysia. As you point out in your message, Bill, morphological and ecological characteristics of the two species do not overlap--ever. Furthermore, while we did not test any, the habitat differences between the two species imply an additional host of physiological and biochemical differences between them. All of that is why we decided to describe E. clarki as a distinct species. To simply invoke an opinion of population differences without any data to support it is merely arm waving. Instead, as you also point out, biochemistry, morphology and ecology are grounded in differences in DNA and, subsequently, proteomics. Such characteristics do not simply all appear or disappear at whim in every specimen in every population.

To come to a conclusion of synonomy without any data is naive and, I'm afraid, bad science. There are many taxonomic issues amongst the elysiids, many of which continually appear on the Forum and in the literature, that have been produced from over 150 years worth of opinions that have ignored data or not even bothered to collect data, but E. clarki is simply not one of them. I too would invite the book's authors to produce some data to support "intraspecific variability" - until then their synyomy is groundless.

Skip

pierce@cas.usf.edu

Pierce. S. K., 2006 (Sep 1) Re: What's wrong with Elysia clarki?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/17695

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