Opisthobranch of the Week Data
Aldisa sp. 2 is considered to be very rare in the waters of Okinawa's main island as I have seen and collected only the above featured animal. The animal was found crawling on the surface of coral rubble located near a wide expanse of open sand dropping off into deep waters.
Aldisa sp. 2 is a moderately-sized dorid nudibranch having gills which can be retracted into a pocket within the mantle. The body feels relatively firm due to imbedded spicules within the skin. The elliptically-shaped mantle is much wider than the foot and has a series of raised dorsal pustules having black centers which are variably sized, but are smaller toward the mantle edge. There are two large dorsal pits, very characteristic of Aldisa spp., one behind the rhinophores and one immediately in front of the gills.
The animal is a dark blood red color with numerous irregular small dots of scattered white pigment. Other than the blood red mantle and black centered pustules, the most noticeable color characteristic of Aldisa sp. 2 is the prominent white edging of the gills. This is the only Aldisa species I've found here with this noticeable gill pigmentation as of the current date.
I've earlier featured two described species of Aldisia found found in Okinawan waters, Aldisa albatrossae and Aldisa pikokai, as well as three additional unknown animals, Aldisa sp. 1, Aldisa sp. 2, and Aldisa sp. 4.
As with other species of Aldisa, Aldisa sp. 2 probably feeds on sponges. Ova were not found associated with the specimen.