Advice for recorders of Flat periwinkles in West Europe.
Dear Recorder,
Littorina obtusata and L. fabalis, the two species of ‘Flat periwinkle’ in U.K., are overwhelmingly entered on iRecord and iNaturalist as L. obtusata, even though L. fabalis is more widespread. This suggests that finds of both are being entered as L. obtusata. Methods for differentiating them are explained in this Flickr album flic.kr/s/aHskPGCpTE but if it is not possible for you to apply them, please enter your records on iRecord as Littorina obtusata/fabalis (iRecord and NBN accept this aggregate entry). Experienced verifiers can identify a few by certain shell forms or, with probability, if certain seaweeds they are found on are in the images. So you might get your ‘Littorina obtusata/fabalis’ redet to one of them. If entering a record of one species, please mention how you differentiated it, but note that the shell forms illustrated in some ‘standard works’ are inadequate or misleading so citing them may not suffice.
If your record came to iRecord from iNaturalist, I regret that the Littorina obtusata/fabalis option is not available on iNaturalist, but your record may be redet. to that before acceptance on iRecord.
Accurately differentiated records of either species in Britain or Ireland (preferably on a spread sheet including if seen live or as empty shell) can be sent direct to the iRecord Verifier/Marine Recorder of Conchological Soc. GB & Ireland at marine@conchsoc.org (Please mention how you differentiated and supply a photo.)
American recorders have it easy as L. fabalis does not occur there.