OKINAWAN
OPISTHOBRANCH OF THE WEEK

Thorunna halourga Johnson & Gosliner, 2001 (11 + 12mm)

Opisthobranch of the Week Data

Taxonomy:

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


Species Account:

        Thorunna halourga is considered to be rare in the waters of Okinawa's main island as I have collected a total of only five individuals. Four additional animals were photographed but not collected. The above featured animals were collected within 5m of one another crawling on the surface of sand amid an area of coral rubble.

        At the time of the original description (Johnson & Gosliner, 2001) the authors reported the species distribution to be limited to Papua New Guinea and the Batangas region of the Philippines. The species is currently reported on the Sea Slug Forum (Rudman, 2002) as being found in Australia (Heron Island), Enewetak Atoll in the Marshall Islands, Japan (both the mainland and Okinawa) and the Philippines. Mike Miller (2003) has recently reported the species from Tulamben, Bali, Indonesia as well.

        I've added a second page showing three additional Okinawa specimens.

        The following information concerning external morphology is taken from Johnson & Gosliner (2001):

The body color ranges from a light purplish-pink to a deep purple. This purplish color is darker at the posterior and anterior ends of the animal, where a thick white mantle margin begins. The mantle margin is slightly undulate and opaque, but may become more translucent at the edges. The foot is darker in color than the rest of the body. The rhinophores and gills range from a light almost white to orange or dark red. In the darker animals, the rhinophores and gills are darker as well. The rhinophores are translucent at the bases and dark reddish at the tips. The color pattern of the area in between the translucent and reddish portion is highly variable. On the rhinophores of some specimens there is a purple band present and in others a white band, and some have both bands. There is no evidence of mantle glands anywhere on the animal, but miniscule glands may be present around the mantle margin. Arranged in a chevron-like pattern, on the dorsum, there are spaces where calcium carbonate spicules were present. Calcium carbonate structures are often lost after fixation of the specimens in Bouin's solution. The spicules are visible in the living animals.

        Thorunna halourga is the only member of the genus Thorunna having a purple mantle and a wide, white mantle border. T. halourga is one of six described species of Thorunna known from Okinawan waters. The six species are:

Etymology:

Literature Cited:


Page Date: 23 Feb '04
Page Modification Date: 23 Feb '04
Digitally manipulated photo
Copyright © 2004 Robert F. Bolland