Opisthobranch of the Week Data
Dermatobranchus cymatilis is considered to be very rare in the waters of Okinawa's main island as I have seen and collected only the single above featured animal. It was collected from Horseshoe Cliffs (Onna area) on the 20th of July, 1994 from 175 feet of water. It was found on a small patch of Halameda alga at approximately 9am.
This animal was previously seen in Gosliner, et al, 2008 (as Dermatobranchus sp. 10, p. 312, top photo). The authors of a recent paper (Gosliner & Fahey, 2011) have now described the animal and the featured animal is the holotype*. I've also added a second page w/ several additional images of D. cymatilis.
The following information on external morphology and remarks are taken from Fahey & Gosliner (2011):
External morphology: The body shape of the living animal is broad, flattened, and narrows at the posterior end. The foot does not project beyond the distinct mantle margin. There is a series of longitudinal dorsal ridges. The oral veil extends forward and has blunt extensions at the corners. The wide-spaced rhinophores are behind the oral veil. They have a series of longitudinal lamellae on the rounded club. The stalk does not narrow noticeably. Marginal sacs are visible along the mantle edge. Approximately one quarter of the way down on the right side of the body is the genital opening. The anus is situated approximately one-third of the way from the posterior end of the body.
The ground colour of the dorsum and foot is opaque white, although the foot has a blue margin. There is a pinkish-orange patch about midway on the dorsum that extends the width of the dorsum. Along the mantle margin and perpendicular to the edge, there are dark rays of colour that extend both downward onto the foot and upward into dark patches along the mantle edge. The dark patches extend up and across the dorsum as broken, dark bands. The dorsal ridges have dark crests, although the colour is broken along the length of the ridges. The rhinophore stalk is white and the club is dark. The oral veil is opaque white with dark perpendicular rays. There is an orange margin along a dark patch on the posterior side of the veil, close to the body.
Remarks: There are several Dermatobranchus species with white ground colour and dark crested dorsal ridges [D. striatus Hasselt, 1824 (Fig. 15I), D. dendronephthyphagus (Figs 30H, 42A), and D. semistriatus (Baba, 1949: pl. 30, fig. 111)]. Dermatobranchus cymatilis has dark patches and 'rays' of dark coloration along the mantle edge and dark perpendicular lines along the foot edge. These rays of dark colour are absent in D. striatus, D. semistriatus, and D. dendronephthyphagus. The yellow coloration on the posterior portion of the oral veil of D. cymatilis differs from the fine orange margin of the veil found in D. semistriatus, D. striatus, and D. dendronephthyphagus. In addition, D. semistriatus has scattered small black spots on the notum, oral veil, and foot that are absent in D. cymatilus [sic]. Although the two species have a similar radular formula, D. cymatilus [sic] has much longer cusps on the radular teeth with fewer denticles on the teeth. The only other species with blue and yellow or orange colour on the oral veil is D. caeruleomaculatus. In this species, the blue spots are on the oral veil and the mantle margin, whereas in D. cymatilus [sic] the blue pigment is on the foot margin. The two differ internally as well. In D. caeruleomaculatus, the jaws have a smooth masticatory margin whereas those of D. cymatilus[sic] are denticulate. Additionally, the inner lateral tooth of D. caeruleomaculatus is smooth whereas that of D. cymatilus [sic] is denticulate.
The radular morphology of D. cymatilis differs from all the externally similar species, but is similar to that of D. semilunus. Both D. cymatilus [sic] and D. semilunus have a broad radula, but D. cymatilus [sic] has many more teeth per half row (67) than does D. semilunus (30-34). In both of these species, the rachidian tooth has a much narrower base and a very prominent central cusp that is much longer than the central cusp of the rachidian tooth. In both species the inner lateral teeth have an elongate central cusp that is much longer than the adjacent denticles and the remaining teeth are devoid of denticles. In D. cymatilus [sic], the outermost teeth are elongate but sharply curved whereas in D. semilunus they are straighter and more acutely pointed. The rachidian tooth of D. primus Baba, 1976 is also narrower than most other Dermatobranchus and it has a long, pointed median cusp. However, the first lateral tooth is not denticulate as found in D. cymatilis. The reproductive system is also similar between D. cymatilus [sic] and D. semilunus. In D. cymatilus [sic] the penial sheath and vagina are far narrower than in D. semilunus.
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. cymatilis - The featured animal above (Holotype*) D. albus D. caeruleomaculatus D. dendronephthyphagus D. diagonalis D. fasciatus D. fortunatus D. funiculus D. gonatophora D. oculus D. ornatus D. primus D. rodmani
*Holotype: See "Type" Dictionary for explanation.