Further information on the Melibe

Dear Nashina,
I think we still have quite a bit to learn about this genus. Unfortunately two characters we use a lot in nudibranch taxonomy, the colour and shape of the radular teeth aren't available in Melibe because they do not have a radula and their colour is quite variable. It also seems the juveniles may look quite different from adults. Terry Gosliner (1987) has given us an excellent summary of our knowledge of the group.

What I think we need now is some studies of populations in a particular geographic areas so we can get a better idea of the variation in shape between juveniles and adults and the variation in colour, shape of cerata, and degree of papillation, within a population. Without that knowledge it is very difficult to decide how many species there are.

For example Baba (1949) identified a species from Japan as Melibe papillosa de Filippi, 1867 but Odhner (1936) and Gosliner(1987) consider that this is a synonym of M. pilosa Pease, 1860. We can't really resolve many of the problems because the original descriptions were not detailed enough, and we don't know how variable the various characters are. One very useful clue could be adult size. You mention your animal animal only grows to 4 or 5 cms. If this its limit then it is unlikely to be the same as a species which c an grow to three or four times that length.

Your mention of its swimming motion is also interesting. There are quite a few observations of species of Melibe swimming. By flattening their cerata and their oral veil vertically, they can swim quite effectively through the lateral flexion of their body. A fairly clumsy, but quite effective way to escape from a non=swimming predator. A related animal Bornella anguilla uses this method to swim, and does it so effectively that it has been given the name 'anguilla' which is from a Latin word for an eel.

Best wishes,
Bill Rudman.