Opisthobranch of the Week Data
Notobryon wardi was initially described from Queensland, Australia, and the species is also known from Japan and South Africa. There is a fair amount of confusion concerning the number of Notobryon species and Bill Rudman commenting in the Sea Slug Forum, is at the present time, putting all photos which seem to represent species of Notobryon on a N. wardi page. Bill feels that it is possible that more than one species is represented there. Quoting from Rudman (2000) in the Sea Slug Forum he points out the following:
Baba (1937) described two more species from Japan, one of which (N. bijecurum), he said differed from N. wardi mainly in having unequal sized mantle lobes, the anterior being larger than the posterior pair. The significance of this feature is unknown as Baba had only a single specimen, and the only study of multiple specimens (Thompson & Brown, 1981), doesn't address this point. Notobryon is closely related to Scyllaea pelagica and Crosslandia viridis*. It differs from both in lacking a median tooth in the radula and from Crosslandia, in having a medio-dorsal posterior crest, which is absent in Crosslandia. Both Scyllaea and Notobryon have a medio-dorsal posterior crest, and both use it when disturbed as a 'paddle', to swim by vigorously waving it from side to side. Like Scyllaea, it has dendritic gill-like processes on the inside of the mantle lobes, especially in larger specimens.
Notobryon wardi is considered to be very rare on Okinawa's main island as I have seen and collected a total of only three individuals. Two of the three collected specimens (33mm & 57mm from 40m) were found within 20cm of each other in an area of mixed sand & coral rubble. I've added a second page illustrating images of the three Okinawa-collected specimens. The Okinawa-collected specimens were not found associated with any particular food but Gosliner (1987) reports that it feeds on campanularid hydroids.