Opisthobranch of the Week Data
I've not personally seen Cuthona purpureoanulata here in the waters of Okinawa's main island and Atsushi Ono mentions (pers. comm.) seeing only the above featured individual in the Keramas* and of course considers the species to be very rare there. Atsushi also reports the above featured animal was found amid dead coral in five meters of water off Zamami Island.
Cuthona purpureoanulata was originally described by Baba (1961) as Catriona purpureoanulata. Baba's original description was based on several specimens collected from Seto, Kii, Japan and Tannowa, Osaka Bay, Japan. The following description of the species is taken from Baba's 1961 publication:
Animal 6-10 mm in length. Cephalic tentacles and rhinophores smooth. Branchial papillae long fusiform, disposed in 11-13 simple oblique rows on each side, 4-5 in the largest rows, the foremost 3-4 rows belonging to the right liver (and the left partner). Genital orifice below the middle of the right liver rows, the anus just in front of the 1st right row of the posterior liver, the nephroproct moderately preanal. Foot-corners rounded. Coloration distinctive in having a purple band down the tip of each of the branchial papillae. Two bands of purple occur also on cephalic tentacles and rhinophores each. General ground-colour translucent whitish, part of head and back covered with clusters of opaque white (or yellowish) dots. The two structures of the head also opaque white towards the tip. The cap of the branchial papillae opaque white, each papilla having a dark brown liver diverticulum. Foot margins sometimes with a fine line of purple.
Jun Imamoto (2001) has several excellent images of Cuthona purpureoanulata from Suruga Bay, Japan, posted on the Sea Slug Forum. In addition to records of the species from Japan, Rudman & Darvell (2001) report finding this animal in Hong Kong as well.
In addition to the above featured animal I've previously featured on these pages the following species of Cuthona:
C. acinosa C. diversicolor C. ornata C. pupillae C. sibogae C. yamasui C. sp. 1 C. sp. 2 C. sp. 3 C. sp. 4
* Keramas = the Kerama Islands Group, located 30 ~ 40 kilometers west of the Okinawa capitol, Naha.