Opisthobranch of the Week Data
Thuridilla albopustulosais a relatively small elysiid and is considered to be uncommon in Okinawan waters; I've not personally seen nor collected any specimens and it is unknown from Okinawa Island, but it has been photographed and collected by Atsushi Ono in the Kerama Islands. The close proximity of the main island of Okinawa to the Kerama Islands, as well as the similar opisthofauna to that of the Kerama Islands, suggests the possibility that it is also present here on Okinawa proper. The above featured animal is one which was photographed in the waters of Gahi Island, one of a series of islands in the Kerama Islands Group, which are located 30 ~ 40 kilometers west of the Okinawa capitol, Naha. This featured animal was photographed and collected by Atsushi Ono on 14 December, 1999, from the waters off the SE Area of Gahi Island, in 5m of water. Atsushi's photograph is used here with his kind permission; the species is considered to be uncommon in the Kerama Islands (Ono, via per. comm., reports seeing more than ten individuals).
Gosliner (1995) named the animal based on the white pustules present on the parapodia. He supplies the following description of external morphology:
The living animals are light blue with scattered black pigment especially near the foot at the base of the parapodia. The parapodial margin is opaque white. The parapodia are covered with scattered opaque white or cream spots or longitudinal bands. The head has diffuse black pigment along its margins. The basal third of the rhinophores is opaque white. The outer two-thirds is bright red with a scattered patch or two of opaque white in the middle of the red. The red pigment extends further basally on the outer side of the rhinophore than on the inner side. This creates the appearance of a diagonal rather than transverse band. The anterior margin of the foot is blue.
The nearest-resembling sacoglossan to Thuridilla albopustulosa found in Okinawan waters is T. vatae (this is relatively common here, but unfortunately I have only a very poor quality image of a 3mm juvenile shown here). Gosliner (1995), in his comparison of the two species, makes the following comments:
Aspects of the coloration of T. vatae differ consistently from that of T. albopustulosa. In T. vatae, the ground color is a dark grey to black while that of T. albopustulosa is blue. The parapodia of T. vatae are ornamented with black and yellow spots, while those of T. albopustulosa are white or cream. In T. vatae, white pigment covers most of the length of rhinophores and only the apex is red. In T. albopustulosa, the majority of rhinophores are red rather than white. In T. vatae, the red pigment is a solid transverse band, while in T. albopustulosa the red is a diagonal band with white patches within the band.