Opisthobranch of the Week Data
Cuthona diversicoloris a small attractive tergipedid and is considered to be very rare in Okinawan waters; I've not personally seen nor collected any specimens and it is unknown from Okinawa's main Island, but it has been photographed 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 by Atsushi Ono during March of 2001, from the waters off Gahi Island, in 7m of water. Atsushi's photograph is used here with his kind permission; it should be noted that Atsushi considers the species to be very rare in the Kerama Islands in as much as he has seen only three animals, 3mm, 5mm, and 7mm (pers. comm.).
Cuthona pupillae was originally described by Baba (1961) as Catriona pupillae. Baba's specimens (a series of animals collected from Osaka Bay, in mainland Japan.
The following description of external morphology is taken from Baba (1961):
Animal always small, 3-5 mm in total length. With cephalic tentacles and rhinophores, the latter slightly longer and smooth. Branchial papillae short, of an inflated fusiform, arranged in 4-6 simple oblique rows on each side, about 3-4 in the largest rows, the foremost 2 rows belonging to the right liver (and the left partner). Genital orifice situated below the 1st row on the right side, the anus in front of the 3rd row on the same side, the nephroproct closely preanal. Foot corners rounded. General body colour translucent whitish, covered with opaque white dots on head and back. Cephalic tentacles and rhinophores nearly always marked with an orange yellow band at about the middle of their length. Branchial papillae with an opaque white cap and a band of the same colour down the tip; liver diverticulum within the papillae, dark brown.
Additionally, Jun Imamoto has a series of photos of this uncommon little animal posted on his site.
There are seven described species of Cuthona featured on these pages as of December, 2007, found in Okinawan waters. The seven are:
C. acinosa C. diversicolor C. ornata C. pupillae The above featured animal C. purpureoanulata C. sibogae C. yamasui