The common periwinkle, or Littorina littorea, is a small marine snail that is commonly found in rocky intertidal zones. As it is a popular organism for ecological and evolutionary research, there are many synonyms or alternative names for the species, including rough periwinkle, blue periwinkle, sea periwinkle, and edible periwinkle. These different names are often used regionally, and can sometimes cause confusion when discussing the species. However, no matter the name, the common periwinkle is an important organism in coastal ecosystems and has several unique adaptations to thrive in its environment.