The Common Periwinkle (Littorina littorea) is a small marine (saltwater) gastropod mollusc in the Littorinidae family of whelks and sea snails. 

The Common Periwinkle has a thick, dark, grey-brown shell, that is sometimes banded. The inside of the shell is chocolate brown. It has 6-7 whorls. It has gills that enable it to breathe underwater. It has a lid on its shell, called an operculum.