Known only from Japan
Mie, Shima Pref. Japan (Kii Peninsula east coast). Depth: 3 m. Length: 5 mm. Jan. 2000. Photo: Yasuhiro Shirai
Known only from the original description:
'Length about 6mm. With perfoliated rhinophores which are quite unusual in the genus Favorinus. Cephalic tentacles as usual. Fusiform [cerata] in 6-7 groups on either side, about 9 in first, 7 in second, 4 in third, 3 in fourth and 2-1 in last groups, the foremost 2 groups standing on horseshoes, the rest forming mere onbique rows. ..... Foot corners tentaculiform. Body pale rose, the [cerata] veined with rose-red, the rhinophores dark. masticatory edge of jaw-plates as in preceding species. Radula formula 18 x 0.1.0. median cusp of the central tooth smooth or with less than 5 denticles. Loc: Amekisho, Sagami Bay, 16-20 m (July 1936 & August 1940, 3 sps.)'
The only character of much value is the perfoliate shape of the rhinophores. The colour of the cerata is often dependent on the colour of the most recent eggs the animals have eaten, and the only other colour information - rhinophores dark - could mean black or perhaps dark pink. At the suggestion of Atsushi Ono, I have tentatively identified a perfoliate species from Japan, with black perfoliate [lamellate] rhinophores, as F. perfoliatus.
Baba, K. (1949) Opisthobranchia of Sagami Bay collected by His Majesty The Emperor of Japan. Iwanami Shoten, Tokyo. 194 pp., 50 Pls.
Rudman, W.B., 2005 (April 29) Favorinus perfoliatus Baba, 1949. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/favoperf