Opisthobranch of the Week Data
Jorunna alisonae is considered to be very rare in Okinawan waters as I have never seen a specimen during numerous years of Okinawa diving and Atsushi reports seeing only the above featured animal which was found on the underside of dead coral in seven meters off Gahi Island, one of a series of islands in the Kerama Islands Group, which are located 30 ~ 40 kilometers west of the Okinawa capitol, Naha.
The following description of external morphology and remarks concerning Jorunna alisonae is taken from Camacho-Garcia and Gosliner (2008).
External morphology: Body oval. Dorsum covered with caryophyllidia* about 133 mμ long. Caryophyllidia elongate, with long spicules. Twelve tripinnate branchial leaves and 10 lamellae in rhinophores in both specimens of 9 and 10 mm preserved length. Oral tentacles conical. Anterior portion of foot notched, grooved.
Background colour pale grey, with numerous grey dots of different sizes on mantle margin. Two lines of spots nearly forming two vertical lines arranged from rhinophores to gills. Viscera visible in the centre of dorsum. Rhinophores cream-brownish with a pale grey-brownish club. Gill grey to dirty brown with some cream glandular spots. Ventral part of animal, the same colour as dorsum. Posterior end of foot visible dorsally when animal moves.
Remarks: The holotype has not been dissected; it is well preserved and of creamish colour. There are caryophyllidia all over the dorsum. There are 15 bipinnate branchial leaves. We could only count about six lamellae in the rhinophores, which are strongly retracted into their rhinophoral sheaths. The penial papilla is partially everted. Jorunna alisonae (Marcus, 1976) can be differentiated from J. tomentosa, a similar species from the northeastern Atlantic, Mediterranean and South Africa, by the presence of jaw elements, a single denticle on the outermost teeth that is present in some specimens, and tripinnate branchial leaves.
According to Marcus (1976), the presence of a single denticle close to the tip on the outermost lateral teeth in J. alisonae may be a malformation. Among the several specimens examined in this study from Hawaii and the Marshall Islands, we found a single denticle present in only one. We conclude that its presence is not a malformation, but a variable feature of this species.
Gosliner et al (2015, p. 197) depict a 35mm individual of Jorunna alisonae. In addition, there are several on-line sites featuring images and data for J. alisonae. These include Bill Rudman's Sea Slug Forum, Scott and Jeanette Johnson's Underwater Kwajalein, and Cory Pittman and Pauline Fiene's Sea Slugs of Hawaii.
I've featured on these pages the following species of Jorunna from Okinawan waters: