Are Aegires punctilucens and A. exeches different?

July 12, 2005
From: Bill Rudman

While reading Fahey & Gosliner's (2004) interesting paper on Aegires I was puzzled by one of their new species, Aegires exeches. This is the animal from the Indo-West Pacific which many authors have identified with the Atlantic species Aegires punctilucens. After carefully reading their description and arguments I can't agree that there are grounds for considering there to be two species. For further information, I have posted, in separate messages, copies of d'Orbigny's illustrations [#14230] and Alder & Hancock's [#14231] of A. punctilucens.

It is probably best to address each of Fahey & Gosliner's reasons in the order they appear in the remarks section of their description of  A. exeches [pp 659-660].

Body shape: "A. exeches has a very elongate body with extremely elevated, unique tubercles ... they are nearly mushroomed shaped, with a flat crown and completely cover the dorsum."   From photos on the Forum, including ones I have just posted [#14229 ], the tubercles of Indo-West Pacific animals are spaced in quite regular arrangements, and the typical colour pattern, which is on the dorsum, is hardly ever obscured. More importantly, the shape of the tubercles is plastic, sometimes a tubercle will be rounded at the tip, but it is capable of opening out to form a flattened top [see #14229]. This would also explain the difference in tubercle shape in d'Orbigny's and Alder & Hancock's illustrations of  A. punctilucens. 
Rhinophore shape: "rhinophores of A. exeches have bifid apices whereas ... A. punctilucens do not"  Alder & Hancock's illustration shows that A. punctilucens can have bifid apices, identical to those of the Indo-West Pacific animal. It is possible that this bifid tip only occurs in larger animals or perhaps the rhinophore has to be fully extended before it is visible, but whatever the situation, it has definitely been reported in both Atlantic and Pacific populations.
Gill protective cover: "A. exeches has a very elaborate, lobed gill structure ..... A. punctilucens has three simple tubercles". Fahey & Gosliner rely on Schmekel & Portmann's (1982) illustration to define this character but there seems to be considerable variation in this character from a simple three small tubercles to the elaborate raised structure found in some Japanese specimens [message #9012], which is essentially 3 tubercles on a raised platform. The photo of the holotype of A. exeches [see Fact Sheet] and the animal from Sydney [see #14229] are essentially three large lobes and are no different from the arrangement seen in a specimen from Norway illustrated by Bakken & Evertsen (2004).
Colour: Fahey & Gosliner consider A. punctilucens has many more iridescent eye spots than A. exeches, but the number and size of these spots is very variable as can be seen in two specimens from Japan photographed by Jun Imamoto [#9013 - many small spots] and [#9012 - few large spots]. The colour of the spot ranges from blue to green, and the surrounding band ranges from orange to light brown in both the Atlantic and the Pacific. Small black spots around the edge of the brownish band are also present in all populations. The only character I am not sure of is the presence of small white spots in some Atlantic specimens. Such spots are present in some Pacific specimens as well [#9012] but are not always obvious.
Reproductive system: It is unfortunate that Fahey & Gosliner had no Atlantic specimens, so they could not directly compare Atlantic specimens with Pacific material. Considering the very diagrammatic drawings of Schmekel & Portmann I would think it is important to re-examine the anatomy of a number of specimens from both the Atlantic and the Pacific before we can be sure there are consistent differences.
Radula: "Schmekel & Portmann illustrate an inner lateral tooth which is much smaller than the rest of the teeth in the row. They also state that the teeth increase in size outwards. In A. exeches, the first three radular teeth are smaller than the remaining teeth."  I think Fahey & Gosliner misinterpret Schmekel & Portmann's description. Schmekel & Portmann only illustrate tooth 1 and tooth 10 but their description does not say tooth 1 is much smaller than the rest, they say in fact that they graduallly increase in size. Templado et al (1987) illustrate the radula of A. punctilucens and it shows, as in most species of the genus, a few smaller inner teeth gradually increasing in size to a maximum about two-thirds of the way out and then a small decrease in size. I have discussed this in an earlier message [#9037] where I posted SEM photos of the radula of a southeastern Australian specimen. These all match the SEM photos of A. exeches on the species Fact Sheet. The difference in radula formula mentioned by Fahey & Gosliner 14 x 11.0.11 for a 4 mm specimen of A. exeches against Schmekel & Portmann's 16 x 18.0.18 for a 6 mm specimen of A. punctilucens is too little information for comparison. With such small specimens the error in comparing the lengths is insurmountable and one specimen from each population is too small a sample. Templado et al give a formula of 15 x 18.0.18 for a 7 mm long specimen, and my Sydney specimen had a formula of 15.0.15 (unfortunately length unknown). I don't believe there is any good evidence in the radula to separate A. exeches from A. punctilucens.

I may be wrong, but in my opinion we have no evidence to show that the Atlantic and Pacific populations are distinct species. There is considerable variation in tubercle development and colour pattern within the Pacific population, and some animals match Atlantic animals. Combining that with the ability of the tubercles to change shape makes any attempt to differentiate species on fine detail of colour pattern and tubercle development very difficult if not impossible. The differences in body shape and tubercle development we can see in Aegires villosus [see photos on Fact Sheet] suggest that such variability is not uncommon in species of the genus.

I would welcome others comments, and in particular some more information and photos of Atlantic specimens. I would just like to reiterate that I greatly respect Shireen Fahey and Terry Gosliner's work, but there are a couple of aspects of this paper with which I disagree. For those of you watching from the sidelines, this is how our science advances. A scientist's job is to develop and propose new ideas and hypotheses, but we also have a duty to present opposing  views when we disagree.

• D'Orbigny, A. 1837. Memoire sur des especes et sur des genres nouveaux de l'ordre des nudibranches, observes sur les cotes de France. [Guerin's] Magasin de Zoologie, (7. Class 5): pp. 1-16, pls. 102- 109.
• Fahey, S. J. & Gosliner, T. M. (2004) A Phylogenetic Analysis of the Aegiridae Fischer, 1883 (Mollusca, Nudibranchia, Phanerobranchia) with Descriptions of Eight New Species and a Reassessment of Phanerobranch Relationships. Proceedings of the California Academy of Sciences, 55, (34): 613–689, 82 figs., 4 tables (Appendix).
• Schmekel, R. L., & Adolf Portmann. (1982) Opisthobranchia des Mittelmeeres, Nudibranchia und Saccoglossa. Fauna e flora del Golfo di Napoli 40, Monografia della Stazione Zoologica di Napoli. pp. i-viii, 1-410, pls. 1-36. Springer-Verlag
• Templado, J., Luque, A. & Ortea, J.A.. (1987) A new species of Aegires Loven, 1844 (Opisthobranchia: Doridacea, Aegiretidae) from the Caribbean Sea: Aegires ortizi spec. nov., with comparative descriptions of the North Atlantic species of this genus. The Veliger, 29(3): 303-307.

Best wishes
Bill Rudman

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