OKINAWAN
OPISTHOBRANCH OF THE WEEK

Gymnodoris tuberculosa Knutson & Gosliner, 2014 (12mm)
Photo by Atsushi Ono

Opisthobranch of the Week Data

Taxonomy:

Frequency on Okinawa: Collection Data:
[brackets indicate range for all Okinawa-collected specimens of the species]


Species Account:

        Gymnodoris tuberculosa is considered to be rare in Okinawan waters. Atsushi Ono reports (pers. comm.) seeing only three animals and I've personally never seen the animal in the waters of Okinawa's main island. Atsushi considers the animal to be very rare in waters of the Keramas.* The above photograph was taken by Atsushi from the waters of Gali Island on the 4th of March, 2008 and he reports finding it between dead corals and rocks. Atsushi's photographs are used here with his kind permission.

        The following description of external morphology and discussion is taken from Knutson & Gosliner (2014):

        EXTERNAL MORPHOLOGY.- The living animals are uniformly translucent white in color and covered in small, rounded tubercles. While these tubercles are obvious in the living animal, they are not always apparent in preserved specimens, depending on the method of preservation. The tubercles seem to preserve well when fixed with Bouin's solution, but not always when fixed with alcohol. The internal organs can be seen through the translucent skin. The color of the digestive gland varies and has been observed as bright orange to pink to brown, perhaps due to the diet of the animal.

        The rhinophores are lamellate with between 8 and 13 lamellae and range in color from translucent white to cream or pale yellow. The gill branches are the same color as the body of the animal and consist of approximately 9-13 main branches arranged in a complete circle with the anus located at the center. They are located close to the center of the length of the animal in the posterior half of the body. In preserved specimens, the gill may appear to be in the posterior third of the body. The genital opening is located on the right side of the animal approximately one third of the length of the distance between the back of the rhinophores to the gills. There is a deep groove in the anterior portion of the foot, ventral to the mouth.

        The specimens examined have spicules embedded in the skin. The spicules can be seen through the skin in some of the photos and are present in the preserved specimens. These spicules vary greatly, in one specimen, there are spicules that have a pink tinge to them while others appear colorless. There also appears to be different morphologies for the spicules within a specimen. Some of the larger spicules were "T" or "Y"-shaped and approximately 0.2 mm long, others were smaller and rod-shaped.

        DISCUSSION.- Gymnodoris tuberculosa differs from other described species of Gymnodoris by its general translucent white color, and the presence of translucent white tubercles. The other species of Gymnodoris that possess prominent tubercles have tubercles that are pigmented, often from yellow to orange to red in color such as Gymnodoris aurita (Gould, 1852), or Gymnodoris ceylonica (Kelaart, 1858). The vagina of this species has a wide bulbous portion similar to that depicted for Gymnodoris inornata, (Bergh, 1880). The depiction of part of the reproductive system of Gymnodoris alba (Bergh, 1877) has a smaller, less pronounced, but similar structure.

        In a personal communication from Vanessa Knutson (Jan, 2015) she mentioned that images taken by Atsushi appear to be that of G. tuberculosa.

        It should be noted that in addition to the examined morphology, the molecular makeup of the described G. tuberculosa was examined by Knutson & Gosliner (2014). Without specimens of G. tuberculosa the species determination of the Ono animals is of course not one hundred percent.

        I've added a second page with two additional images of Gymnodoris tuberculosa and as of the current date (February, 2015) I've previously featured the following described and undescribed species of Gymnodoris from Okinawan waters on these pages:

Etymology:

Literature Cited:


        * Keramas = the Kerama Islands Group, located 30 ~ 40 kilometers west of the Okinawa capitol, Naha.


Page Date: 01 Feb '15
Page Modification Date: 01 Aug '15
Digitally manipulated photo
Copyright © 2015 Robert F. Bolland