Opisthobranch of the Week Data
Doriopsis pecten is considered to be very rare on Okinawa; I've personally collected only two individual animals, however, the above featured animal was photographed here on Okinawa by Mr. Yukinobu Adachi * and the image of this little dorid is taken and modified from his Marine Photography Page, Light and Dark ( see "Slug Collection"), and is used here with his permission.
D. pecten is certainly unique for Okinawa as it is the only dorid found here in possession of the distinctive blue color associated with the species. The species has a wide Tropical Indo-Pacific distribution and is known to feed on siliceous sponges (Marshall & Willan, 1999); Gosliner (1987) points out the species is found on a blue-black sponge upon which it feeds and both the coloration of the nudibranch and its egg mass are virtually identical. Remarkably, both of the collected Okinawan animals were found during mild currents, drifting in the plankton within a meter of the bottom, composed of mixed silty-sand and coral rubble.
There is apparently a fair amount of confusion in the literature in terms of the number of Doriopsis species within the genus. The following are comments taken from the Sea Slug Forum (Rudman, 1999) in regards to some of the confusion:
Species of Doriopsis are characterised by the arrangement of the gills in a transverse line across the back rather than in the typical dorid circle. Specimens of Doriopsis are either deep blue, green or yellow and there has been considerable confusion in the literature concerning how many species there are in the genus. At one extreme 4 species, one each of green and blue and two of yellow have been suggested, while at the other extreme only one variably coloured species has been proposed.
Biological observations from throughout the Pacific suggest that there are at least two species, one yellow or green and one deep blue. It is also possible that the yellow New Zealand species, Doriopsis flabellifera Cheeseman, 1881, is a third valid species. The earliest name for the yellow/green species is D. granulosa and for the blue, D. pecten. Reports from Hawaii (Kay & Young, 1969; Bertsch & Johnson,1981), Japan (Hamatani, 1961, Baba & Hamatani, 1961), central Pacific (Young, 1967; Johnson, 1981) show that D. pecten feeds exclusively on a deep blue sponge Terpios, and D. granulosa on a yellow or orange sponge, identified by Young (1967) as Prianos phlox de Laubenfels, 1954. The eggs of D. granulosa are reported to be yellow, while those of D. pecten are cream, and the egg ribbon of D. granulosa is about four times as wide as that of D. pecten.
* Background Information on Mr. Yukinobu Adachi: