Onchidoris depressa (Alder & Hancock, 1842) 10mm
Photo by Atsushi Ono

Opisthobranch of the Week Data


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

Species Account:

        Onchidoris depressa is considered to be very rare in Okinawan waters. I'm not aware it has been seen or collected in the waters off Okinawa's main island and Atsushi Ono reports (pers. comm.) seeing only two uncollected animals as of the current date. Atsushi's photographs are used here with his kind permission. The above featured animal was found on the underside of dead coral in the waters off Gahi Island in the Keramas*. Both photo show the animal as found on its host(?) bryozoan food.

        The following description of Onchidoris depressa is taken from Bill Rudman's Sea Slug Forum (2003):

Onchidoris depressa is a flattened, ovate animal, which is probably often overlooked because of its excellent camouflage on the encrusting bryozoan colonies on which it lives and feeds. The mantle is translucent clear with scattered red-brown spots, especially in the mid-region, and covered with tapering translucent soft papillae. It can gave a glistening appearance form the crowded glassy spicules which are usually visible through the mantle skin This species seldom reaches more than 9mm in length. The rhinophores are sparsely lamellate and there can be up to 12 simple gills arranged in a circle around the anus. In the British Isles it is reported to feed on the bryozoan Schizomavella linearis. Alder & Hancock report the spawn to be 'pinkish'.

        I've added a second page with an additional image of the featured animal. On these pages I've previously featured another described onchidoridid, Diaphorodoris mitsuii as well as a single undescribed onchidoridid, both of these photographed by Atsushi.

Literature Cited:

        * Keramas = the Kerama Islands Group, located 30 ~ 40 kilometers west of the Okinawa capitol, Naha.

Page Date: 01 Aug '14
Page Modification Date: 01 Aug '14
Digitally manipulated photo
Copyright © 2014 Robert F. Bolland