Flat periwinkle  (Littorina obtusata)

This species is common on all British shores where brown seaweeds are found (3). It has a wide distribution in north-west Europe (2) and is found from Northern Norway to the south of Spain and is absent from the Mediterranean (4) (3).

This periwinkle is closely associated with brown seaweeds, especially Ascophyllum nodosum, Fucus vesiculosus and Fucus serratus on which it feeds. It occurs on the mid-shore to lower tidal levels and may occasionally occur in the sublittoral (2).