Opisthobranch of the Week Data
Marianina rosea is considered to be very rare in Okinawan waters; I've not seen the animal here on Okinawa's main island and Atsushi Ono mentions (per. comm.) having seen only two members of the species in the Keramas*, the above featured animal and an additional uncollected 3mm individual. The above animal was collected by Atsushi during April of 2000 from the surface of a rock on a coral reef.
I've taken the following information concerning the species from Marshall & Willan (1999):
This is a small dendronotoid nudibranch with a long and slender body. The dorsum is high and rounded in profile. The foot is approximately the same width as the mantle and it ends in a long tail with a pointed tip. The anterior foot corners are enlarged into prominent, slender, sharply pointed tentacles. The oral tentacles are large, slender, and tapering to a pointed tip. The rhinophores bear numerous long papillae all over and they therefore resemble an upraised hand (palmate). Each rhinophore is surrounded by an elongate, tubular sheath with simple margins that is drawn out into a spike laterally. The body bears up to four clusters of cerata, there being only two cerata per cluster and the clusters being arranged strictly in pairs. The cerata are smooth, curving upwards, and they taper to a pointed tip (fusiform). The general body colour is uniformly pinkish lilac and there is a white streak mid dorsally on the tail. The basal quarter of the oral tentacles is magenta and the rest is opaque white. The rhinophoral sheath is magenta basally and the tip is cream. The rhinophoral clavus is blood red to pale orange The cerata are uniformly cream. Marianina rosea is unique because of the structure of its cerata. At first glance it will inevitably be mistaken for an aeolid because of the small size, long oral tentacles and tentacular foot corners, but the palmate rhinophores with their sheaths indicate its affinity with the rest of the members of the dendronotoid family Tritoniidae **. There is little variation in general colouration within populations of M. rosea on the Great Barrier Reef. Marianina rosea feeds on hydroids. It deposits a white spawn mass on its food hydroids.
* Keramas = the Kerama Islands Group, located 30 ~ 40 kilometers west of the Okinawa capitol, Naha.
** RFB is following both Rudman (2000) & Gosliner (1987) in placement of the species in the Family Marianinidae.