July 28, 2001
From: Bernard Picton
I'll attempt to offer some light on the Flabellina species in the N Atlantic. Many of the species actually occur on both sides of the Atlantic. On the European side we have all of the American species, but some do not extend as far south as the British Isles and Jussi Evertsen is familiar with them so he can help with this. The amphiatlantic species seem to occur in Iceland and Greenland and may maintain continuous populations across the Atlantic - they seem to be the more cold-tolerant species.
Southern distribution limits in the NE Atlantic (European side) are:
Flabellina verrucosa - southern limit Irish Sea
Flabellina salmonacea - southern limit Norway
Flabellina gracilis - south to Atlantic coast of France
Flabellina pellucida - southern limit W Scotland - I've found one specimen in Ireland (in Lough Hyne, almost the warmest place here - I wouldn't believe it until I checked the radula!)
Flabellina nobilis - previous southern limit Norway, Faeroes - I have one unpublished Irish record - a single juvenile specimen but I'm fairly positive about the identification.
Also - not found on American side of Atlantic:
Flabellina borealis - southern limit North Sea
Flabellina browni - south to Atlantic coast of France
Flabellina lineata - south to Mediterranean
Flabellina pedata - south to Mediterranean
There has been taxonomic confusion over these species and occasionally I'll check the radula but I think I can normally distinguish living animals OK.
Flabellina borealis is a bit of an unknown as far as living appearance goes but Jussi and I just looked at a sample of animals caught in the North Sea by Anne Dewicke of Univ. of Gent, Belgium and they are quite distinctive in their ceratal arrangement. The cerata are unclustered and taper in size to very small ones which are numerous at the sides and in an extensive region at the tail end, extending very near to the tip of the tail. The painting by Lemche in Just and Edmunds, 1985 shows an animal with clustered cerata and I think this is a misidentification. With hindsight I think Walton's 1908 report of animals from the North Sea identified as Coryphella salmonacea were probably F. borealis. Anne caught the animals in a hyperbenthic sledge at 70 m depth just north of the Dogger Bank, they were 'white and orange-red' in colour and the bottom was soft mud and detritus. There were over 500 individuals in the sample - Ann describes it thus: 'When the sledge came up and was still hanging outside, we were wondering what those orange-red beasts could be. They were so brightly coloured that we all thought they might be a sort of shrimp! '
I attempted to make a key to identification of N Atlantic Flabellina on external living characters. Jussi Evertsen simultaneously sent a similar key to the Forum, so at your suggestion we have prepared a joint version. We have not included Flabellina parva and Flabellina islandica as we have no personal experience of living animals of these, but the other 9 species should separate all right.
firstname.lastname@example.orgPicton, B.E., 2001 (Jul 28) Flabellina in the North Atlantic. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/4733
Thanks for your thoughts on these animals and the various photos you have sent recently which show distinguishing characters not already illustrated on the Forum. It has been a necessary preparation for the posting of this key.