OKINAWAN
OPISTHOBRANCH OF THE WEEK

Pleurobranchus albiguttatus (Bergh, 1905) 20mm
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:

        The following species description is taken from Marshall & Willan (1999):

The mantle of this large pleurobranch is sufficiently thick to prevent the viscera from being discerned from above. The mantle bears numerous, tightly packed, low pustules. The central axis of the gill (rachis) bears prominent pustules as in all species of Pleurobranchus. A triangular, pale area (pedal, or metapodial gland) is present on the undersurface of the tail in sexually mature individuals.
Colouration varies from orange to brown and the mantle is mottled with cream. A few of the pustules are opaque white and spotted with brown so they appear to be elevated above the rest. The foot is spotted with orange or brown.
The tips of the rhinophores pulsate continuously in life.
Pleurobranchus albiguttatus could easily be mistaken for P. peroni, but the foot sole of that species is unspotted. The reproductive systems must be dissected in order to confirm the identity. P. albiguttatus could be confused with P. nigropunctatus, currently considered endemic to South Africa, but that has tall papillae scattered between the pustules.
Pleurobranchus albiguttatus feeds on compound ascidians at night; individuals are generally found hiding during the day. The spawn consists of a white, spirally-arranged mass with one edge attached to the substrate and the other (the upper edge) very wavy. This spawn mass looks like that of a nudibranch.

        Pleurobranchus albiguttatus is currently unknown from the waters of Okinawa's main island and Atsushi Ono reports (per. com.) seeing in excess of ten animals in the Keramas. The above featured animal was found and photographed on the rope of a buoy by Atsushi in January of 1999 from Agonoura Bay, Zamami Island, Kerama Islands Group, located 30 ~ 40 kilometers west of the Okinawa capitol, Naha. Atsushi has kindly furnished the above image of this 20mm animal and is used here with his permission.

        See also a second page with images of two additional representatives from the Keramas.

        There are to date the following six described species of Pleurobranchus known from Okinawan waters, as well as several undescribed species.

Literature Cited:


Page Date: 15 Jul '02
Page Modification Date: 02 Jul '12
Digitally manipulated photo
Copyright © 2012 Robert F. Bolland