Opisthobranch of the Week Data
Aegires exeches is considered to be very rare on Okinawa as I have seen and collected only the above single individual. The above featured animal is a paratype specimen (CASIZ* 115394). Following the dive, the animal was found in a sorting pan, the contents of which originally held a series of green and red thallophytes, including a series of feather-like hydroids. The collection habitat was one of mixed sand and coral rubble. Prior to the description of A. exeches by Fahey & Gosliner (2004) the above animal was featured on the Okinawa Slug Site as Aegires punctilucens.
The following description of external morphology and remarks concerning Aegires exeches is taken from Fahey & Gosliner (2004):
EXTERNAL MORPHOLOGY.-- The body shape is elongate and the posterior end of the foot ends in a point. There are numerous compound tubercles projecting from the dorsum, such that the body appears to be composed completely of tubercles. The tubercles are elongate and narrow slightly before mushrooming into a flattened plate-like top. From the flattened tops, multiple spicules protrude. The rhinophore pockets are very long and are composed of two main tubercles on the anterior side, two shorter tubercles on the posterior side and much smaller tubercles in between. The rhinophores are smooth and have bifid apices. The gill protective appendages are also composed of elaborate tubercles. The gill leaves themselves are small, inconspicuous and tripinnate.
The background color ranges from white to tannish-white. The tops of the tubercles on the tan specimens have dark spots. The specimen from Enewetak, Marshall Islands is completely white. It has three evenly spaced, pale tan rings around the rhinophores. The tan specimens have three to four blue spots on the dorsum. These spots are arranged symmetrically, with two just posterior to the rhinophores, one at the centerline in front of the gill and the forth at centerline just posterior to the gill.
REMARKS.-- Externally, Aegires exeches most closely resembles A. punctilucens from the Mediterranean. However, there are both external and internal differences that separate these two species. The most obvious external differences are the body shape, rhinophoral apices, gill protective structure morphology and tubercle arrangement. Aegires exeches has a very elongate body with extremely elevated, unique tubercles. That is, they are nearly mushroom shaped, with a flat crown and completely cover the dorsum. D'Orbigny also described the body shape of A. punctilucens as being elongate, with a broadening at the midpoint. He described the tubercles of A. punctilucens as conical, with a flattened top, and a definite symmetry to their arrangement. Schmekel and Portmann (1982) also illustrated and described the tubercles on the specimens from the Mediterranean as being much shorter and wider at the base and symmetrically arranged, such that there are smooth parts of the dorsum visible between them. In A. exeches, no smooth spaces exist between the tubercles, which are taller, narrower at the base and more densely arranged than on A. punctilucens.
The rhinophores of A. exeches have bifid apices whereas the rhinophores of A. punctilucens do not (see Schmekel and Portmann 1982 for an illustration).
The gill protective structure of Aegires exeches is also different from that of A. punctilucens. Aegires exeches has a very elaborate, lobed gill structure, while A. punctilucens has three simple tubercles (see Schmekel and Portmann 1982 for a drawing of the Mediterranean specimens).
When comparing the external coloration, both species can be white or light brown. But Schmekel and Portmann describe minute opaque white dots spotted over the brown color, and the iridescent "eye" spots have a brownish-red circular area around them, bordered with black-brown dots. Specimens of Aegires exeches from Okinawa, Hawaii and the Marshall Islands do not have any opaque white dots over the dorsal color, but do have iridescent spots, although in much fewer numbers than is found on A. punctilucens. The "eye" spots on A. exeches can also be surrounded by a border of black-brown dots and a smooth orange circle surrounding the center as seen in photos on the Sea Slug Forum (Rudman 2004).
There are significant differences in the reproductive morphology between these two species. Although D'Orbigny didn't describe or illustrate the reproductive organs of A. punctilucens. Schmekel and Portmann drew the anatomy of specimens from the Mediterranean. Most noticeably, A. exeches has a receptaculum seminis that attaches to the base of the bursa copulatrix. In A. punctilucens the receptaculum connects directly to the bulbous vagina. The prostate of A. exeches is short, tubular and nearly as thick as the ampulla, whereas in A. punctilucens the prostate is very thick and sausage-shaped and very coiled. Aegires exeches has a very long, tubular ampulla, a narrow vagina and a long, thin vaginal duct. A. punctilucens has a very bulbous ampulla and a very wide vagina, with a thick vaginal duct.
There are two differences in the radular teeth between these two species. Schmekel and Portmann illustrate an inner lateral tooth that is substantially smaller than the rest of the teeth in the row. They also state that the size increases outwards. In A. exeches, the first three lateral teeth are smaller than the remaining teeth, which are all the same size. In A. exeches, the radular formula is 14 x 11.0.11 for a 4 mm specimen. Schmekel and Portmann give a radular formula for a 6 mm specimen of 16 x 18.0.18.
Baba (1974) described a specimen found in the Sado district of the Japan Sea as Aegires punctilucens. Comparison of Baba's drawings and description of that specimen to our specimens of Aegires exeches leads us to believe that Baba's specimen is also A. exeches.
Whereas A. exeches bears same external similarities to the Mediterranean A. punctilucens, the Indo-Pacific specimens clearly represent a distinct species.
I've added an additional image of Aegires exeches (3mm), photographed by Atsushi Ono in the waters off Zamami Island, Keramas.**
I've previously featured on these pages the following species of Aegires from Okinawan waters:
* CASIZ = California Academy of Sciences Invertebrate Zoology.
** Keramas = the Kerama Islands Group, located 30 ~ 40 kilometers west of the Okinawa capitol, Naha.