Periwinkles are 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.They have a shell that is smooth and brown to brownish-gray in coloration and up to about 1 inch long. The base of the shell is white. Periwinkles may live out of the water for several days and can survive in challenging conditions. Out of the water, they can stay moist by closing up their shell with a trapdoor-like structure called an operculum. Periwinkles are mollusks. Like other mollusks, they move around on their muscular foot, which is coated with mucus. These snails may leave a trail in the sand or mud as they move around.The shells of periwinkles may be inhabited by a variety of species and may be encrusted with coralline algae. Periwinkles have two tentacles that can be seen if you look closely at their front end. Juveniles have black bars on their tentacles.
