The common periwinkle or winkle (littorina littorea) is a species of small edible whelk or sea snail, a marine gastropod mollusc that has gills and an operculum, and is classified within the family littorinidae, the periwinkles.this is a robust intertidal species with a dark and sometimes banded shell. it is native to the rocky shores of the northeastern, and introduced to the northwestern, atlantic ocean. there is another snail known as the small periwinkle or melarhaphe neritoides that looks similar, but is smaller.

Source: Wikipedia