Aegires exeches is a distinct species

July 13, 2005
From: S. Fahey & T. Gosliner

Dear Bill,
Thanks very much for posting the recent messages regarding Aegires. You're right about how science advances by exchanging ideas and publishing testable hypotheses. It's one of the most dynamic aspects of science and can be the most stimulating part of our work. I have posted our comments on the family name in a separate message [#14254 ].

Concerning your comments on whether Aegires exeches and Aegires punctilucens  are distinct species [message #14248 ]. We think that the two can be distinguished externally, although the internal morphology is where the greatest differences lie.
1. Dorsal tubercles: Aegires punctilucens has far more densely packed dorsal tubercles than are found in Aegires exeches. These tubercles are clearly mushroom-shaped in A. exeches as opposed to the flattened or rounded tops of the tubercles of A. punctilucens that do not extend outwards from the base. We think that the photos you have posted of the Sydney harbor specimens may indeed be A. exeches, but could also have been A. punctilucens introduced from Europe. Also, the tubercles of A. exeches have far more spicules that protrude substantially such that the animal has a "fuzzy" appearance. The tubercle character states utilized for our analyses (#5, #6) were coded the same for A. exeches and A. punctilucens so the tree topology was not affected by this character. All the photos on the web (including Picton's very nice photo), d'Orbigny's drawing and Alder and Hancock's drawing do not show spicules that protrude significantly as in A. exeches specimens from the Indo-Pacific.
2. Rhinophore shape: Although the bifid tip may be apparent in some older (larger) specimens of A. punctilucens, this character (#10) was not included in the final phylogenetic analysis, so it had no effect on the outcome of the tree topology.
3. Rhinophoral tubercles: In A. punctilucens the rhinophoral tubercles are simple while in A. exeches there are secondary branches on the base of the larger tubercles
4. Gill protective appendage: The more elaborate gill appendage found in A. exeches differs from A. punctilucens. The Japanese specimen displays this elaboration, as does the specimen from Sydney harbor, which as we note above, may indeed be A. exeches. We don't believe that the photo of Bakken and Evertsen (2004) is of A. exeches although the gill appendage has a similar, though distinct morphology. This character did not influence the result of the analysis, since both species were coded with the same character state (#20, #61).
5. Color: We agree that some Atlantic specimens would have been nice to examine for our study, but we wanted to present the information at hand in our publication. As always, any contributions of specimens and discussion are welcome! Nevertheless, the dorsal color characters including the ocellae (#54, #55, #57) were all coded as similar states for the two species and thus did not affect the outcome of the phylogeny presented.
6. Reproductive system: We agree that Schmekel and Portmann's (1982) drawing on page 99 is diagrammatic, but we used their rather detailed drawing on page 389 as a comparison for the specimens we examined. There are several reproductive differences between the Indo-Pacific (A. exeches) and Atlantic (A. punctilucens ) specimens. To summarize from our publication:
a) The receptaculum seminis attaches at a different point on the vagina in each of the two species A. exeches vs. A. punctilucens (at the base of the bursa vs. directly into the vaginal duct);
b) The distal end of the vagina has a very different morphology between the two species (long and narrow vs. short, large and bulbous),
c) The vaginal duct morphology (long and straight vs. short and curved),
d) The prostate (curved and wide vs. very thick and straight) and
e) The ampulla (narrow and slightly curved vs. thick and tightly bowed).
f) Penial bulb (short and narrow vs. long and very thick with a distinct distal thickening)
7. Radular morphology: Schmekel and Portmann's drawing shows a much wider tooth shape than we found in the Indo-Pacific specimens, which all had much narrower, "candy cane"-shaped teeth. Although in both species the teeth gradually increase in size outwards, in A. exeches there are at least three substantially smaller, narrower teeth before the teeth gradually increase in size (see Fig. 60C). We provided the radular formula of A. exeches as a comparison for A. punctilucens but radular formula was not used as a character in our phylogenetic analyses to determine the relationships among Aegires.

To summarize, we believe that it is the combination of characters that can be used to distinguish between species, not just one, two or three differences. The data matrix that we used had over 60 characters for consideration.
Finally, we would certainly like to examine specimens from the Atlantic and Mediterranean, or would love to see someone take on the project and publish their results for discussion.

Thanks again for taking the time to critically examine our manuscript,  Bill. Regards,
Terry and Shireen

sfahey@calacademy.org

Fahey, S. & Gosliner, T., 2005 (Jul 13) Aegires exeches is a distinct species. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/14253

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