Periwinkle (Littorina sp) any small marine snail of the family Littorinidae, found in large numbers along rocky shores in the intertidal and low subtidal zones on the shores of Europe and eastern North America. Periwinkles have a conical spiral shell, and feed on algae.

Periwinkles reach about 1 inch (2.5 cm) in length, and when harvested, are transported live. Periwinkles are benthic grazers rather than filter feeders so they do not concentrate the toxin of PSP (Paralytic Shellfish Poison). They are mobile and graze on algae.

Periwinkles have been harvested since the early 1950's in the Maritimes, the 1987 catch amounted to 220 tons. The price to fishermen was about $1.00/kg.

The harvesting is accomplished by hand picking during low tide. Picking is done by fishermen and their families and often by students to supplement their incomes.

Most periwinkles are transported live. If meats are to be extracted they are boiled in salt water or steamed for 6-8 minutes and extracted by hand. The main market is ethnic Japanese communities in large North American cities such as New York, Boston, Montreal, etc. European markets also exist.