Periwinkle, a small sea animal with a thick spiral shell. There are about 80 species of periwinkles, widely distributed in cold and temperate climates. They are found in large numbers on rocks, sea grasses, and wharf pilings. Periwinkles feed on algae and seaweed.

The common periwinkle is found along the coast of northern Europe, the British Isles, and New England. It is ½ to 1 ¼ inches (13 to 32 mm) long. The shell is smooth and is brown or dark gray. The common periwinkle is a popular food in Europe. The rough periwinkle is found along the coast of northern New England. It reaches a length of ½ inch (13 mm) and has a yellowish-gray shell with rows of grooves. The smooth periwinkle, found along the coast of southern New England, is ½ inch long. It has a smooth shell that is yellowish-brown with a dark spiral band.

Periwinkles belong to the family Littorinidae of the mollusk class Gastropoda. The common periwinkle is Littorina littorea; rough, L. saxatalis; smooth, L. obtusata.