Opisthobranch of the Week Data
Hypselodoris apolegma is considered to be uncommon on Okinawa. Although only ten specimens have been collected since March of 1984, I've seen and photographed perhaps an additional half dozen individuals. There is quite a bit of confusion as to the validity of the species and Rudman (2002) on the Sea Slug Forum features a photograph by Phil Slosberg of H. bullocki and H. apolegma mating. This suggests that H. apolegma may well be a color form of H. bullocki which exhibits a fair amount of color variation as shown on the Sea Slug Forum.
I've taken the following information concerning the original species description from Yonow (2001):
Description.- . . . is recognized by its almost luminescent magenta pink to violet mantle, the colour being connected to an opaque white margin by a region of violet stippling combined with white reticulations. The mantle is elongated, fairly spatulate anteriorly, and the edge is crinkled; these characters remain in the preserved specimens. The body is high and fleshy but firm, and although there is a definite mantle overlap, it is reduced. The foot is also large and firm, and extends beyond the mantle posteriorly. This is visible in the preserved material, where the mantle extends far beyond the foot anteriorly but the reverse occurring posteriorly. The rhinophores are deep orange yellow with purple peduncles; the holotype has 25 lamellae on the club. . . . the lamellae meet in an alternating series, rather than opposite each other, and there are 27 lamellae on one side and 29 on the other. The five tripinnate gills are yellow with violet stalks, located far back on the dorsum, and held very high. Both the rhinophores and gills issue from a pocket with a raised rim, which has the same colour as the mantle. Both pocket rims are particularly prominent, in life as well as in the preserved material. The gill pocket is very high in life, almost tubular, and is pimpled; these pimples are present immediately surrounding the gill pocket and extending forward beyond the 2/3 mark on the dorsum and remain on the preserved specimens. The foot is uniformly coloured, a shade more purple than the mantle, with no banding around the edge. Ventrally, the foot is bilaminate: neither lamina is notched, although the edges are crumpled. In all three preserved specimens, the folds of the sides of the foot are characteristic, with a main fold just beyond the head, and smaller undulating folds subsequently. The oral tentacles are just visible far on each side of the head.
I've added a second page with four additional images of this attractive chromodorid from Okinawan waters.
The above featured animal is one of thirteen described species of Hypselodoris found in Okinawan waters. The thirteen species identified to date (July, 2011) are: