Grey shell with partial white band from well defined site where previous workers found 100% of Rough periwinkles were Littorina arcana (Dytham, Grahame & Mill, 1990).
Though perhaps not statistically significant, among over 20 000 Rough periwinkles at seven sites, they found only ten grey ones with a white band which they identified as L. arcana; specimen Z had a partial white band on a grey shell.

Other identification criteria used for specimen Z

Ribbed orange ciliated field along edge of prostate. See L. arcana Z1002 06Littorina arcana Z1002. Dissected male from 9.9 mm high shell. N. Yorkshire, September 2014. Specimen Z. .

No full account yet of this species.
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