Flabellina in the North Atlantic

July 28, 2001
From: Jussi Evertsen

Dear Bernard and Bill!
It is great to see that there is great interest in the north Atlantic species of Flabellina. I must first be allowed to say that I prefer the use of Coryphella, as I explain on my website at http://www.ntnu.no/~vmzotbak/nudibranchia

I have myself had the opportunity to have collected and studied most of the species mentioned in Bernard's mail, except F. islandica, F. parva and F. browni. When identifying species of Flabellina it might in the beginning be quite confusing with cerata sticking out everywhere and rhinophores and white rings and oral tentacles to look for. But I have in my own experince found three reliable features to keep in mind; the arrangement of the cerata, the placement of the anus, and the shape of the rhinophores. One thing I have found to be impossible to use as a good feature, is colouration, except for F. pedata and F. lineata. The use of rings or white tips of the cerata can be very variable, as can be seen in F. verrucosa (which also has a list of synonyms as long as a full roll of toilet paper), and also the shape of the cerata. Also the colour of the cerata (or the digestive glands to be precise) seems to vary according to what the nudibranch is feeding upon. I have seen variable colouration of the cerata in F. verrucosa, F. gracilis, F. pedata, and F. nobilis. I can but confirm Bernard's observation on F. pellucida having a liking to Eudendrium (all three species actually). Also the shape of the cerata is very variable, especially in F. verrucosa. It seems to be three distinct groupings of Flabellina from north atlantic waters concerning ceratal arrangement; those with a continous arangement of the cerata along the sides of the back (as seen in salmonacea, borealis and partly in F. nobilis), those with cerata set on a common stalk (F. pedata and F. pellucida) and those with cerata arranged in distinct groups (with or without further arrangement of cerata in each group in clear rows; see F. verrucosa). The shape of the rhinophores and localisation of the anus seems to be both distinct and shared features between the species, but are useful tools when identifying the species. So far I have not yet seen any Flabellina species with lamellate rhinophores as seen in species within Flabellina from the Mediteranean and tropic.

Attached is a "field-key" which is an amalgamation of a key that I have been using and regularly modifying, and one that Bernard Picton has developed for his own use. Clearly the best way to identify these animals is to look at their anatomy but this is not always practical and of little use in the field or in identifying photos. So we hope this key will be useful for anyone trying to identify their North Atlantic Flabellina.

Yours sincerely
Jussi Evertsen
Trondhjem Biological Station
Norwegian University of Technology and Science

jussie@stud.ntnu.no

Evertsen, J., 2001 (Jul 28) Flabellina in the North Atlantic. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/4876

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