The Common Periwinkle Profile

The common periwinkle (Littorina littorea), also known as the edible periwinkle, is a frequent sight along the shoreline in some areas. Have you ever seen these little snails on the rocks or in a tide pool? Despite the large numbers of periwinkles on the U.S. shoreline today, they are not a native species in North America but were introduced from western Europe. These snails are edible — would you eat a periwinkle? Description Common periwinkles are a type of marine snail. 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. Classification Kingdom: AnimaliaPhylum: MolluscaClass: GastropodaSubclass: CaenogastropodaOrder: LittorinimorphaSuperorder: LittorinoideaFamily: LittorinidaeSubfamily: LittorininaeGenus: LittorinaSpecies: littorea    Habitat and Distribution Common periwinkles are native to western Europe. They were introduced to North American waters in the 1800s. They were brought over possibly as food or were transported across the Atlantic in the ballast water of ships. Ballast water is water taken in by a ship to make sure operating conditions are safe, such as when a ship discharges cargo and needs a certain amount of weight to keep the hull at the right water level. Now common periwinkles range along the eastern coast of the U.S. and Canada from Labrador to Maryland and are still found in western Europe. Common periwinkles live on rocky coastlines and in the intertidal zone, and on muddy or sandy bottoms. Feeding and Diet Common periwinkles are omnivores  that feed primarily on algae, including diatoms, but can feed on other small organic matter, such as barnacle larvae. They use their radula, which has tiny teeth, to scrape the algae off of rocks, a process which can eventually erode the rock. According to a University of Rhode Island article, the rocks on the coastline of Rhode Island used to be covered with green algae, but have been bare gray since periwinkles were introduced to the area. Reproduction Periwinkles have separate sexes (individuals are either male or female). Reproduction is sexual, and females lay eggs in capsules of about 2-9 eggs. These capsules are about 1mm in size. After floating in the ocean, the veliger hatches after a few days. The larvae settle on the shore after about six weeks. The lifespan of periwinkles is thought to be about 5 years. Conservation and Status In its non-native habitat (i.e., the U.S. and Canada), the common periwinkle is thought to have altered the ecosystem by competing with other species, and grazing on green algae, which has caused other algae species to become overabundant. These periwinkles can also host a disease (marine black spot disease) which can be transferred to fish and birds. References and Further Information Buckland-Nicks, J., et. al. 2013. The living community inside the common periwinkle, Littorina . Canadian Journal of Zoology. Accessed June 30, 2013.littoreaEncyclopedia of Life. Littorina . Accessed June 30, 2013.littoreaGlobal Invasive Species Database. Littorina littorea. Accessed June 30, 2013.Jackson, A. 2008. Littorina . Common periwinkle. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 01/07/2013]. Accessed June 30, 2013.littoreaReid, David G., Gofas, S. 2013. Littorina . Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?ptaxdetailsid140262. Accessed June 30, 2013.littorea (Linnaeus, 1758)University of Rhode Island. Common Periwinkle. Accessed June 30, 2013.