August 2, 2007
From: Bill Rudman
Concerning message #20146:
When discussing Gigantonotum album I should have mentioned Inoue & Okutani (1987) which described specimens of what appears to be the same animal from Suruga Bay on the Pacific side of Honshu, Japan. They have identified their specimens as Pleurobranchella nicobarica Thiele, 1925 and describe its internal anatomy which conforms with what is known from the original description. As I mentioned before, little is known of the anatomy of Gigantonotum except for the radula which is reported to have a central radula tooth - absent in Pleurobranchella. Because the external shape of Gigantonotum and Pleurobranchella is so similar, it seems likely that the report of the central tooth in Gigantonotum was an error but it would be nice if Alexei Chernyshev's specimen could be checked because of it was found closest to the type of Gigantonotum.
If we accept Inoue & Okutani's identification, Pleurobranchella nicobarica will have a wide distribution from Japan, west to South Africa [as Pleurobranchoides gilchristi O'Donoghue, 1929, and the Red Sea [as Pleurobranchoides sp. Eales, 1938]. In Japan it has been found at depths of between 200-400 m, and has a soft gelatinous translucent body when alive. It is found quite commonly by fisherman operating crab trawlers.
Inoue, R. and Okutani, T. (1987) Pleurobranchella nicobarica Thiele, 1925, new to the Japanese Notaspidea fauna. Venus, The Japanese Journal of Malacology 46: 219-225.