Opisthobranch of the Week Data
Dermatobranchus fortunatus, a small arminid nudibranch, is considered to be very rare on Okinawa as the above featured animal is the only individual I've personally found here as of this writing (mid-August, 2001). The animal was collected from a vertical rock wall at the edge of the reef; the wall, overlooking fifty-five or so meters of water, was covered with numerous cnidaria, pofifera, and miscellaneous encrusting organisms. The original image was recorded at 2:1 and the resulting edited image is unfortunately not very sharp. Atsushi Ono has an excellent image of a pair of 10mm individuals on his web site; Atsushi's site features opisthobranchs from the Kerama Islands Group, which are located 30 ~ 40 kilometers west of the Okinawa capitol, Naha.
Marshall & Willan (1999) report the species (as D. fortunata) to be common in the waters of Heron Island (Heron and Wistari Reefs) and that adults were found throughout the year. In as much as I haven't Bergh's original description of the species on hand, I've taken the following description on external morphology and remarks from Fahey & Gosliner (2011):
External morphology: The specimens examined from Papua New Guinea match Bergh's (1888) description and drawings of his specimens collected from Indonesia.
Remarks: Bergh (1888) provided only a brief description of external morphology, the radula, and the reproductive system. The external pattern of dorsal markings shown in Bergh's figure (Fig. 1G) closely matches that of the present material. With regard to reproductive anatomy, Bergh drew only the penis of this species. He showed the penis to be conical and enlarged from the prostate. The specimens we examined did not have an enlarged penial sheath. The radular morphology of the specimens we examined matched Bergh's drawings and description. This species is one of the more commonly encountered species of arminids in the Indo-Pacific tropics. . . . it is widespread from the western Indian Ocean to the Central Pacific of the Marshall Islands.
As of the current date (Early-April, 2014) thirteen described species of Dermatobranchus from Okinawa's main island and the Keramas are featured on these pages. These thirteen species are:
In addition, I also have a series of undescribed Dermatobranchus species from local waters.
D. albus D. caeruleomaculatus D. cymatilis D. dendronephthyphagus D. diagonalis D. fasciatus D. fortunatus - The featured animal above D. funiculus D. gonatophora D. oculus D. ornatus D. primus D. rodmani