White penis filament clearly visible above animal’s back; long, slender, steadily tapering to a non-mucronate tip. Not anaesthetised; see P8560.

Other identification criteria used for specimen M

Previous work by Hannaford Ellis on the same shore as this find showed that L. arcana were thin-shelled, heavily ridged and multicoloured with tessellations or bands. The shell of this specimen fits the description (see M8540). In contrast, L.saxatilis s.s. had thick smooth unicolorous shells. N.B. these shell differences only apply on this shore; neighbouring shores had different shell characteristics that did not enable segregation of the spp.

Ribs on shell have sloping surface with raised adapical edge (distinguishes from adult L. compressa).

Furrows between shell-ribs are wide and shallow (distinguishes from L. compressa).
See M8540 01 Littorina arcana M8540. 13mm high. N.W. Anglesey, Wales. March 2014. Specimen M.

No full account yet of this species.
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