Opisthobranch of the Week Data
Tritonia sp. 2 is considered to be very rare on Okinawa's main island as the above featured animal is the only individual which I've seen. It was found crawling on the surface of coral rubble at the base of a vertical rock wall covered with numerous invertebrates; it was collected during a mid-morning dive.
Tritonia sp. 2 would appear to be identical to a 14mm animal depicted in Marshall & Willan (1999, fig. 234, p. 247, as Tritonia sp. 1). The authors report the Australian distribution to be Queensland and New South Wales. Also, Gosliner (pers. comm.) mentions the animal is also known from Papua New Guinea. This of course implies a wide geographic range for this undescribed species in the tropical Western Pacific. The following partial description of this animal is taken from Marshall & Willan (1999, p. 129):
This is a moderately large dendronotoid nudibranch with a long and slender, smooth body. The dorsum is high and flattened in profile with a distinct lateral ridge. The foot is slightly wider than the mantle and it ends in a long narrow tail with a pointed tip. The anterior foot corners are rounded and not expanded.
The oral veil is developed into two tentaculate lobes, one on either side. There are about five major tentacles arising from each lobe and all of them bear a few slender papillae. The rhinophores bear numerous long papillae and they therefore resemble an upraised hand (palmate). Each rhinophore is surrounded by an elongate, tubular sheath with a simple flanged margin. The ridge on the body bears 11 pairs of branched gills, alternately horizontal and vertical. The two largest pairs are in the centre and the gills become progressively smaller anteriorly and posteriorly from that region. The gills almost disappear in the vicinity of the tail.
The general body colour is opaque white with a series of large, translucent, lozenge shaped patches down the back coinciding with the bases of the gills. These patches allow the orange viscera to be clearly seen. The foot is translucent with white speckles. The tentacles on the oral veil, rhinophoral sheath and gill stalks have translucent orange streaks. The rhinophores and gills are white.
I've previously featured several tritoniid species from Okinawan waters. Tritonia bollandi is the only confirmed species of the genus known from Okinawa's main island as of the current date. In addition to the above featured animal I've previously featured Tritoniid sp. 1, from the Kerama Islands.