Stylocheilus nomenclature

June 11, 2000
From: Ángel Valdés

Dear Bill,

I was reading your discussion with Richard on Stylocheilus nomenclature with great interest. But I think you are talking about two different things here.

One problem is the whether the species names Stylocheilus longicauda and Stylocheilus striatus are synonyms or not. I agree with you that there are probably two different species. A good starting point to solve this problem could be to study the type material of both species. One syntype of Aplysia striata and one syntype of Aplysia longicauda still remain in the collections of the Muséum National d'Histoire Naturelle of Paris. Philippe Bouchet will the delighted to lend the specimens for study.

If we have two different species involved, both names should be maintained and used according to their original meanings (Article 49). The law or priority and the ruling of the Commission have nothing to do with this. The Code is very clear in this respect: names should be applied in the meaning of their name-bearing types. If the name S. longicauda was used for the wrong species, then you should correct the application of the name, as you did. There is no reason to conserve the misapplication of a name unless that misapplication was used as the type of a new genus (Articles 11.10, 67.13, 69.2.4 and 70). And this is not the case.

I agree with Richard that a complete taxonomic study should be carried out before reaching a definitive conclusion, and that study should include the related genus Bursatella. But if you are right (and I think you are), and Stylocheilus longicauda and Stylocheilus striatus are different, then you should go ahead and use the right name for the right species, regardless the consequences it might have.

All the best,


Dear Angel,
I agree that sorting out the identity of the two names and using them correctly, is an act of identification and as such has nothing to do with the Rules. However I also think that identifying the two species can be done independently of sorting out the phylogenetic relationships between Stylocheilus and Bursatella.

Concerning the study of the types in Paris. I wish I could be as confident as you that they would solve the problem. In cases where there is a key character which can survive 150 years of museum preservation then looking at old types is obviously useful. The shell of a mollusc is usually definitive, as are the internal hard parts of primitive opisthobranchs. Sometimes we can be lucky with an old nudibranch type which has a species or genus specific radula, but equally often, as I have found with Risbec material, past preservation and mounting techniques have destroyed the radula.

From the published accounts of the anatomy of the two? species of Stylocheilus, there are no easy characters to use in the genus. The radular morphology of aplysiids, at least at the genus level, is not a very precise character, and in the case of Stylocheilus the gizzard plates show no distinctive differences, and Marcus' early suggestion that the penial spines of S. longicauda (as S. citrina) were smaller than in S. striatus (as S. longicauda), she later decided were a function of age (size) not species.

Personally, I think the available illustrations and descriptions quite clearly define the two species. If the debate is whether there are two species, then we might as well use more recently collected specimens, in which the anatomy is easier to study, and multiple specimens can be compared. If after such an investigation, one or more distinctive characters are discovered, then I think it would be appropriate to borrow the types from Philippe Bouchet and confirm their presence in the types. If distinctive characters can't be found in more recent material then the types may as well rest in peace.

References to anatomical studies can be found on the following pages: 'S. citrina' References  and
S. striatus References.

Best wishes,
Bill Rudman.

Rudman, W.B., 2000 (Jun 11). Comment on Stylocheilus nomenclature by Ángel Valdés. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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