Opisthobranch of the Week Data
Risbecia godeffroyana is considered to be very rare in the waters of Okinawa's main island; the above featured animal is the only individual I've seen here and unfortunately the animal was not collected. This animal was previously listed here on the site as R. imperialis but more recent resources (Rudman, 2001, Marshall & Willan, 1999) suggest that this animal is R. godeffroyana. Both of these resources have material which is very similar in appearance to the above featured animal. Rudman (2001) has several complementary animals posted on the Sea Slug Forum.
The following information concerning morphology, color, and behavior of Risbecia godeffroyana is taken from Marshall & Willan (1999):
This is a moderately large dorid nudibranch that can retract the gills into a pocket beneath the mantle. The body feels soft and slimy. The mantle, which is wider than the foot, is elongate in outline and flattened in profile. The mantle is completely smooth. The tail extends behind the animal when it is crawling. The rhinophores are lamellate. The numerous, large, simple gills are spirally arranged and surround the anus.
The mantle is opaque white with a dense, pale purple reticulum mid-dorsally that is strongest on the head. Around the anterior mantle margin and also in five or six, short, transverse, lateral bars, are dark violet areas with vivid yellow spots. Therefore, the mantle does not have a continuous margin or sub-marginal band. The tail has a dense purple reticulum. The rhinophores have a pale pink stalk and violet clavus with white flecks on the lamellae. The gills are white with thin violet streaks up the outer axes.
When Risbecia godeffroyana is crawling, the gills make vibrating movements and the anterior edge of the mantle is regularly flexed upwards and lowered. R. godeffroyana often occurs in pairs with one animal crawling directly behind the other. The second (and often smaller) animal places its head on the tail of the leading animal.
Risbecia godeffroyana is distinctive in its mantle colouration and it is unlikely to be confused with any other nudibranch. Its behaviour of pairing is shared with R. tryoni.
Risbecia godeffroyana feeds on siliceous sponges. The spawn is unknown.
There are two species of Risbecia currently found in the waters of Okinawa's main island, the above featured R. godeffroyana and R. tryoni.