Juvenile Flabellina from Sweden

Dear Mike,
I asked Bernard Picton and Jussi Evertsen, who jointly prepared the key for North Atlantic species of Flabellina, to have a go at identifying your photo. I have put their replies below. As you can see, it seems a bit difficult to identify them from photos when they are so small. Concerning your question about too many species. Although some species are difficult to separate on general body shape and colour, there are good distinguishing characters to be found in the internal anatomy (including the radular morphology), and probably in aspects of their natural history (food, development time, etc.).

•Comment from Bernard Picton [bernard.picton.um@nics.gov.uk]:
Hi Bill - The Flabellina is a juvenile so very difficult to be certain. From the hefty oral tentacles and short broad-based tail I'd guess that it might be F. salmonacea, if the sender has located a place where there is a settlement of juveniles perhaps they can look again in the spring to see what they grow up into. - Bernard Picton

•Comment from Jussi Evertsen [jussi.evertsen@vm.ntnu.no]:
Hi Bill! - The image looks to me as if it could be a Coryphella, with the long
oral tentacles and distinct footcorners. Also the cerata seems to be arranged in transverse rows and in groups, which excludes species of Coryphella with cerata set one by one (gracilis), and with cerata set in continous rows (nobilis and so forth). Also the individual shown in the picture seems young. I could suggest this species to be either Coryphella verrucosa (rufibranchialis form) or a Coryphella browni as described by Bernard Picton. - Jussi Evertsen

Thanks Bernard and Jussi,
Bill Rudman