Atagema alba (O’Donoghue, 1927)
Atagema alba is one of those California species that is not seen in years, and then someone comes across a population explosion. This has occurred this year in the San Diego and Channel Islands.
This strange little mouse-like dorid is easily identified by the irregular ridge down the midline and the three large extrabranchial lobes anterior to the gill. The fuzzy appearance of the dorsum is produced by caryophyllidia (tubercles with protruding spicules).
Little is known about the species, but I believe it is a sponge eater, like other Atagemas. It has been documented only from Monterey Bay south to Ensenada, Mexico. It has been collected in Scripps Canyon, San Diego at 120 feet (Jim Lance, pers. comm.).
Nice find Steve.
Addenda to Atagema alba by Hans Bertsch:
Atagema alba has been found on the steep cliffs of Arbolitos, Punta Banda, south of Ensenada, Mexico. The walls are brilliantly covered with numerous invertebrates, especially the bright orange cup coral Balanophyllia elegans. The in situ picture of a 38 mm long animal was taken at 45 feet depth, 2 December 1984. I have not seen it since in my southern California/northwestern Baja California water diving. As Dave noted, this rare species ranges from the intertidal to 120 feet deep.
Dave Mulliner took a portrait photo of this animal , illustrating its distinctive features, especially the lobes protruding posteriorly over the gills.
The radula is the typical dorid sponge-eating shape, with smooth, curved hamate cusps. Terry Gosliner and I described the radula , anatomy, synonymy and distribution of this species in our 1986 paper.
Bertsch, Hans, and Terrence M. Gosliner. 1986. Anatomy, distribution, synonymy, and systematic relationships of Atagema alba (O’Donoghue, 1927) (Nudibranchia: Doridacea). The Veliger 29 (1): 123-128.
Hans Bertsch is well known to readers of the SlugSite both from underwater and above water activites. This photo of Rosa and him was taken recently on Gatún Lake, Panama, while on their way to visit the Smithsonian Tropical Research Institute preserve on Isla Barro Colorado.