Re: Phyllidiopsis bayi or Fryeria bayi
March 28, 2002
From: Angel Valdes
Dear Bill,
Thank you very much for your comments on the paper that Terry and I wrote on the phylogeny of the radula-less dorids.
There are three points that I would like to discuss here:
1) The question of the generic placement of Fryeria bayi. - I have examined all specimens of this species collected so far, including the type material from the Paris museum and additional specimens from the Madrid museum. All the specimens examined have a long buccal bulb with microscopic and simple oral glands, and the oral tentacles are fused together. Also, all of them have a ventral anus. As you said Brunckhorst characterized the genus Fryeria on the basis of several anatomical features in addition to the position of the anus, including oral tentacles separated and short buccal bulb with large oral glands. Fryeria bayi is anatomically identical to other species of Phyllidiopsis. Another species of Phyllidiopsis, P. blanca, may have a ventral anus, so there is no question to me that F. bayi should be transferred to the genus Phyllidiopsis.
2) The question of the monophyly of the radula-less dorids.- You are right, our paper is just a preliminary step in trying to understand the relationships of this group of opisthobranchs. We found, based on the observation of anatomical characters and a phylogenetic analysis that the radula-less dorids are a monophyletic group. However, I agree that more information should be collected before a definitive conclusion. Gilianne Brodie is working on histological characters for this group and she is finding similar results. I do not think it is appropriate for me to talk about her work here, but it would be nice if Gilianne could send a note to the Forum with her ideas about this problem. I have also been working on molecular characters (based on the 16S gene) and the conclusion is clear again: the radula-less dorids are monophyletic. I am now in the process of publishing my molecular results. I believe that very soon we would be able to show enough evidence to convince most opisthobranch specialists that the radula-less dorids are monophyletic.
3) The question of the validity of Fryeria.- The variability of the position of the anus in Phyllidiopsis bayi is not the only reason to synonymize Fryeria with Phyllidia. The main reason is that Fryeria, even though is a monophyletic group (once F. bayi is excluded), characterized by the presence of a ventral anus, is a clade nested within the larger Phyllidia clade. Right now we are using a rank-based nomenclatural system so we are not allowed to name monophyletic groups unless we can fit them in a particular category, such as genus, family, etc. At the same time, because of all us believe in evolution, we do not name paraphyletic groups anymore. If Fryeria is maintained as a valid genus, this would render Phyllidia paraphyletic, and this is undesirable. On grounds of nomenclatural consistency Fryeria is regarded as a synonym of Phyllidia. If one day we would be able to agree to a rank-free system of classification we could reinstall the name Fryeria with no rank.
Thanks very much again for your thoughts,
Angel
avaldes@nhm.org
Valdes, A., 2002 (Mar 28) Re: Phyllidiopsis bayi or Fryeria bayi. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/6424Dear Angel,
Thanks for your comments. I am glad we agree on most things. What I find most frustrating is how little anatomical information has actually been published. By information I mean diagrams and illustrations of actual dissections. Even Brunckhorst's extensive monograph (1993) has few anatomical diagrams and usually only the type species of each genus is described. This means that the only way to review such work is to do it again, which is just not practical. For example, there are a number of comparative tables in Brunckhorst which suggest that as well as the position of the anus, there are considerable anatomical differences in the foregut and reproductive systems of Phyllidia and Fryeria. I would like to be able to make my own judgement on that, but the published evidence is not there for me to do so. Similarly with species of Phyllidiopsis, it would be useful if sufficient evidence could be presented to the reader for them to make an 'armchair' judgement on the hypothesis being presented to them. I have searched the literature for some anatomical illustrations of different species which would allow me to get a feel for the similarities and differences but can't find them. One growing problem is that many authors are replacing illustrative information with data matrices and tables of character states. This makes it almost impossible for readers to make a judgement on the hypothesis being presented, unless they are willing to 'trust' the authors to have interpreted the anatomy correctly [NB: I don't include the well-illustrated Valdes & Gosliner, 1999 in this comment]. I realise that illustrations can be 'doctored' but at least if there are detailed illustrations available the reader can see what the author has in mind, and make a judgement on whether they agree with how the author has interpreted the anatomy. Without naming names, I once had a puzzling correspondence with a colleague over the anatomy of an animal. It only became clear when they sent me a diagram of the anatomy, that they had confused part of the reproductive system with the alimentary canal. Easy enough to do, but a fatal and untraceable error, if all a reader has to work on is a character matrix based on an anatomical error.
Sorry I am making this so long. Let's discuss you last point - the 'paraphyly' of Fryeria. I think its a bit early to say we understand the evolution of this group. In your cladistic analysis you only include one species of each genus and one branch of your cladogram ends up with an unresolved trichotomy consisting of Phyllidia varicosa, Fryeria marindica [in the middle] and Phyllidiella pustulosa. You may have later cladograms with more species analysed, but the one in your 1999 paper doesn't look as though the evidence for Fryeria nesting in the middle of a large Phyllidia clade is very strong. Have you published a later analysis with more species?
Best wishes,
Bill Rudman
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