Opisthobranch of the Week Data
I've never personally seen Dermatobranchus fasciatus in the waters of Okinawa's main island however Atsushi considers the species to be common in the Keramas. * He reports (pers. comm.) that he's seen in excess of fifty individuals within the Keramas. The above image of D. fasciatus is used with Atsushi's kind permission. Atsushi mentions finding this small arminid in an area of dead coral and rock.
The following description of both external morphology and remarks concerning Dermatobranchus fasciatus is taken from Gosliner & Fahey (2011):
External morphology: The body shape of the living animal is elongate, flattened, and narrows at the posterior end. The foot does not project beyond the distinct mantle margin. There is a series of low longitudinal dorsal ridges. The oral veil extends forward and the corners protrude slightly. The rhinophores are situated behind the oral veil. They have a series of longitudinal lamellae on the rounded club. The stalk does not narrow noticeably. No marginal sacs were visible. There are no branchial or hyponotal lamellae under the mantle margin. The genital opening is situated about one-quarter of the distance along the anterior body side. The anus is situated approximately half of the way to the posterior end of the body. The ground colour of the dorsum and the foot is opaque white with dark spots scattered randomly. Both the mantle and foot have a pink edge. On the mantle, there are two transverse bands of tan coloration with darker spots scattered randomly within the bands. The bands of dark colour divide the dorsum into approximate thirds. The dorsal ridges are the same white as the ground colour and the depressions between the ridges are grey. The rhinophore stalk is white with some random dark spots and the club is dark brown to black with opaque white spots. The oral veil is opaque white with dark spots and a pink margin.
Remarks: Externally, D. fasciatus most closely resembles D. semilunus from the western Pacific. Both species have an opaque white ground colour with a band of tan or white across the dorsum. Dermatobranchus semilunus has a single u-shaped brown marking whereas D. fasciatus has two broader bands of brown. The rhinophores of D. fasciatus are dark brown to black with opaque white spots, whereas those of D. semilunus have white lines along each vertical lamella.
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:
D. albus D. caeruleomaculatus D. cymatilis D. dendronephthyphagus D. diagonalis D. fasciatus - The featured animal above D. fortunatus D. funiculus D. gonatophora D. oculus D. ornatus D. primus D. rodmani
* Keramas = the Kerama Islands Group, located 30 ~ 40 kilometers west of the Okinawa capitol, Naha.