OKINAWAN
OPISTHOBRANCH OF THE WEEK

Sohgenia palauensis Hamatani, 1991 (8mm)
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:

        Sohgenia palauensis is considered to be very rare in Okinawan waters; only three individuals (6, 8, and 8mm) have been collected by Atsushi Ono (per. comm.) and RFB has seen none directly off Okinawa's main island. The above featured animal was photographed, and collected from Furuzamami Beach, off Zamami Island, in the Kerama Islands, 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 found on a rock amid a coral reef by Atsushi during May of 2001 in 4m of water. Atsushi's photograph is used here with his kind permission. Atsushi also has an additional image of a 6mm specimen posted on the Sea Slug Forum.

        I unfortunately don't have the original description of the species by Hamatani (1991) and I'm therefore using the following species summary of Sohgenia palauensis taken from the Sea Slug Forum (Rudman, 2002):

"Body leaf-shaped and very thin 4.5mm long. Foot undivided and occupies the whole ventral surface of the body. General body colour is grass green due to presence of green pigments possibly derived from the animal's food. The rhinophores are very close together and bifurcate very close to the base. The upper half of the rear branch (of the rhinophores) is tinged slightly with brown. The cerata are stick-shaped with a spherical swelling at the top, wholly transparent and colourless. The stalk can have some minute conical protuberances. No gut branches penetrate into the cerata."

In the original description the cerata are quite a bit smaller and there are no brown spots, but the pericardial hump has two swellings like in these photos*, and the general shape is very similar. It has similarities to a species of Cyerce or Polybranchia which have autotomised most of their cerata, but the swollen tip of the cerata, and the brown pigmentation on the rhinophores is quite unusual for those genera.
        *Comments by Bill Rudman in re a photo from Hachijo Island, Japan, submitted by Shoichi Kato.

Etymology:

Literature Cited:


Page Date: 14 Apr '03
Page Modification Date: 14 Apr '03
Digitally manipulated photo
Copyright © 2003 Robert F. Bolland