Young male L. fabalis.
Found on Fucus serratus. Identification as L. fabalis confirmed by examination of penis. Pure white spirobid like spire frequent on some, but not all, populations of L. fabalis.
Not fully mature, so has almost flat spire, not fully expanded body whorl and thin fragile shell wall found on juveniles of both species.
If only shell features are used for identification, specimens of L. fabalis like this may be mistaken for L. obtusata. Its algal coating might make it seem olivaceous, a colour most usually found on L. obtusata.
Swanage is in on "the south coast of England between Dorset and Kent . . . where discrimination of shells is difficult" (Reid, 1996) so examination of penes is especially necessary for reliable identification.
Swanage, Dorset. April 2016.
Full account at: 02 Differentiation L. obtusata/L. fabalis
39 Differentiation L. obtusata/L. fabalis
