Stylocheilus nomenclature

June 6, 2000
From: Richard Willan

Dear Bill,

Thanks for pointing me in the direction of your change to the name for the common widespread Stylocheilus. You have really opened a can of worms!

Taxonomically, Stylocheilus is not as distinct from Bursatella as you might think and the external characters you mention as distinguishing between the two supposed species of Stylocheilus are not clear cut - juvenile S. longicauda do have very long tails; the papillae are always compound on S. longicauda, and I have slides of a S. longicauda from Daydream Island, Queensland, with no brown lines on the body at all. The colour and size of the ocelli on the body are extremely variable too. It is timely to undertake a study comparing the anatomy of all the "woolly" sea hares and another one investigating the phylogeny of the resulting species.

Nomenclaturally, your change will cause confusion now that both longicauda and striata are in usage. It is good you raised the matter, but I'm not sure if a change in name is actually appropriate at this time, regardless of the biological conclusions. A case for retention of longicauda to the International Commission on Zoological Nomenclature, though lengthy, would have succeeded because it could have been easily proven: (a) the name longicauda was in general usage for the species in question and (b) longicauda has been used as the presumed valid name, in at least 25 works, published by at least 10 authors in the past 50 years, and encompassing a span of not less than 10 years. In other words the case would have been argued as one of reversal of precedence of synonymous names to achieve stability which is explicitly the overarching principle embodied in the present International Code of Zoological Nomenclature which came into effect on 1st January 2000.

Unfortunately I think you need to change your name once again. Quoy & Gaimard originally used the name Aplysia striata. But the gender of Stylocheilus is masculine, so the specific name striatus, -a, -um ,which is a Latin adjective meaning striped or lined, needs to be written in the masculine form, striatus, to be in agreement with the genus.

Richard Willan

Willan, R., 2000 (Jun 6) Stylocheilus nomenclature. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Richard,
Thanks for your comments on Stylocheilus. You raise a number of interesting points.

Gender matching
Firstly the need to change the ending of the name to match the gender. You are of course correct. Personally if we are interested in stability of nomenclature, the need to follow the arcane grammatical rules of Latin, which none of us learn, every time a species is moved to another genus is somethinh many of wish had been changed in the new addition of the Rules. With the increased use of computerised lists and searches, the prospect that the spelling of species names may never be fixed is absurd. This is a case in point. The spelling of striata changed to striatus when it changed genus from Aplysia (feminine) to Stylocheilus (masculine). Without a background of latin grammar you would think that the spelling of longicauda would change to longicaudus but it doesn't, because longicauda meaning 'long tail' is treated as a noun in apposition and so is independent of the gender of the genus name.

Identification of species.
Anyone who has seen true Stylocheilus longicauda has no difficulty distinguishing it from the striate form. It is true that juvenile S. striatus often have a long tail. It is interesting to speculate that this is an adaptation in juveniles to cling on to small weeds so they are not washed away, which is lost in adults. Perhaps Stylocheilus longicauda which is always found in association with floating algae has evolved neotonously from a juvenile benthic species. Whatever its origin, the feature mentioned by all the early describers of this species was not the branched or unbranched papillae but the association with floating algae. In my mind there is no difficulty in identifying Stylocheilus longicauda. There may be more than one benthic species, but if so, that will initially be a question of comparative anatomy and only later a question of nomenclature. You say that I should have applied to the Commission as a case could have been argued "as one of reversal of precedence of synonymous names". In my opinion (and Terry Gosliner's and Clay Carlson's) the names are not synonyms. This is a case of misidentification not nomenclature.

The 'Rules' and the Law of Priority.
You mention that changing the names of these species will cause confusion. Name changes always cause confusion, but it is usually short lived except in the few cases where a name applies to a economically important organism. Much more confusion would occur if the Law of Priority* which underpins all of nomenclatural stability, became something which we could easily be overrule at the urging of a few hidebound taxonomists who don't want to change. Unfortunately taxonomy is the only science where you can't ignore the work of incompetent or sloppy workers. But I don't see why we need to reward them as well. I greatly admire some of the early naturalists who suffered great privations and sometimes, like poor van Hasselt, an extremely early death, but still produced descriptions and illustrations which far surpass many of those that came later from workers who worked with the preserved collections of other people. I don't see any reason to displace the valid identifiable names of diligent field naturalists, just to accommodate incorrect nomenclatural decisions produced in the comfort of Europe and North America years later.

You seem to suggest we have a duty to suppress early names to protect later mistakes. I am afraid I don't agree. Any weakening of the Law of Priority, except in the most exceptional circumstances, would weaken the whole system of nomenclature and lead to endemic instability.

Bill Rudman.

* Law of Priority. The rules on naming organisms is underpinned by one basic tenet, which is that the earliest valid name given to a species has priority over all subsequent names given to the same species.

Rudman, W.B., 2000 (Jun 6). Comment on Stylocheilus nomenclature by Richard Willan. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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