|Periwinkle emerging from its shell, Sweden|
|L. littorea on the edge of a small sandy beach in Woods Hole, Massachusetts|
The common periwinkle or winkle, Littorina littorea, is a species of small edible sea snail, a marine gastropod mollusc that has gills and an operculum, and is classified within the family Littorinidae, the periwinkles.
The shell is broadly ovate, thick, and sharply pointed except when eroded. The shell contains six to seven whorls with some fine threads and wrinkles. The color is variable from grayish to gray-brown, often with dark spiral bands. The base of the columella is white. The shell lacks an umbilicus. The white outer lip is sometimes checkered with brown patches. The inside of the shell has a chocolate-brown color.
As a result of its robust nature, Littorina littorea can be highly variable in phenotype with several different morphs present. Its phenotypic variations may be indicative of a speciation event, as opposed to phenotypic plasticity. This is of particular importance to evolutionary biology, as it presents the possible opportunity to view a transitional phase in the evolutionary life of an organism.
|This section requires expansion. (December 2011)|
Common periwinkles are native to the coasts of northern Spain, Scotland, Ireland, Scandinavia and Russia.
Introductions to North America 
Common periwinkles have been introduced to the Atlantic coast of North America, possibly[vague] by rock ballast in the mid-19th century. The first recorded case was in 1840 in the Gulf of St. Lawrence. It is now a predominant mollusc from New Jersey northward to Newfoundland. It was accidentally introduced to the North American East Coast within the last few centuries and it is now extraordinarily abundant on New England rocky shores. In Canada, their range includes New Brunswick, Nova Scotia, Quebec, Newfoundland and Labrador.
This species is also found on the West Coast of the United States, from Washington to California. L. littorea is now the most common marine snail along the North Atlantic coast. It has changed North Atlantic intertidal ecosystems via grazing activities, altering the distribution and abundance of algae on rocky shores and converting soft-sediment habitats to hard substrates, as well as competitively displacing some native species. The presence of this species has caused extensive damage due to interspecific competition with native intertidal gastropods.
The common periwinkle is mainly found on rocky shores in the higher and middle intertidal zone. It sometimes lives in small tide pools. It may also be found in muddy habitats such as estuaries, and can reach depths of 180 feet.
L. littorea is an omnivorous, grazing intertidal gastropod, primarily on algae grazer, but it will feed on small invertebrates such as barnacle larvae. They use their radulae to scrape algae from rocks, and, in the salt marsh community, pick up algae from the cord grass, or from the biofilm that covers the surface of mud in estuaries or bays.
Life cycle 
L. littorea is oviparous, reproducing annually with internal fertilization of egg capsules that are then shed directly into the sea, leading to a planktotrophic larval development time of four to seven weeks. Females lay 10,000 to 100,000 eggs contained in a corneous capsule from which larvae escape and settle to the bottom. This species can breed year round depending on the local climate. It reaches maturity at 10 mm, and lives five to 10 years.
Human use 
This species appears in prehistoric shellfish middens throughout Europe, and is believed to have been an important source of food since at least 7500 BC in Scotland. It is still collected in huge quantities in Scotland, mostly for export to the Continent, and also consumed locally. The official landings figures for Scotland indicate over 2,000 tonnes of winkles are exported annually. This makes winkles the sixth most important shellfish harvested in Scotland in terms of tonnage, and seventh most important in terms of value. However, since actual harvests are probably twice reported levels, the species may actually be the fourth and sixth most important, respectively.
They are usually picked off the rocks by hand or caught in a drag from a boat. They are mostly eaten in the coastal areas of Scotland and Ireland, where they are commonly referred to as winkles or in some areas buckies, willicks, or wilks. In Belgium, they are commonly called crickles. They are commonly sold in paper bags near beaches in Ireland and Scotland, boiled in their local seawater, with a pin attached to the bag to enable the extraction of the soft parts from the shell.
Periwinkles are considered a delicacy in African and Asian cuisines. The meat is high in protein, omega-3 fatty acids and low in fat; according to the USDA National Nutrient Database for Standard Reference, raw snails in general are about 80% water, 15% protein, and 1.4% fat.
- Linnaeus C. (1758). Systema naturae per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata. pp. [1-4], 1-824. Holmiae. (Salvius).
- Reid, David G.; Gofas, S. (2011). Littorina littorea (Linnaeus, 1758). Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=140262 on 2011-05-16
- Benson A. J. (2011). Littorina littorea. USGS Nonindigenous Aquatic Species Database, Gainesville, FL. http://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=1009 RevisionDate: 4/21/2009.
- Common periwinkle at marlin.ac.uk retrieved 16.10.2008
- Welch J. J. (2010). "The "Island Rule" and Deep-Sea Gastropods: Re-Examining the Evidence". PLoS ONE 5(1): e8776. doi:10.1371/journal.pone.0008776.
- Grahame J. (1975). "Spawning in Littorina littorea (L.) (Gastropoda: Prosobranchiata)". Journal of experimental marine Biology and Ecology 18: 185-196.
- Benson A. (2008). Littorina littorea. USGS Nonindigenous Aquatic Species Database, Gainesville, FL. <http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=1009> Revision Date: 8/20/2007
- Chapman J. W., Carlton J. T., Bellinger M. R. & Blakeslee A. M. H. (2007). "Premature refutation of a human-mediated marine species introduction: the case history of the marine snail Littorina littorea in the northwestern Atlantic". Biological Invasions 9:737-750.
- Chang A. L., Blakeslee A. M. H., Miller A. W. & Ruiz G. M. (2011). "Establishment Failure in Biological Invasions: A Case History of Littorina littorea in California, USA". PLoS ONE 6(1): e16035. doi:10.1371/journal.pone.0016035.
- Polyphenols in brown algae Fucus vesiculosus and Ascophyllum nodosum: Chemical defenses against the marine herbivorous snail, Littorina littorea. J. A. Geiselman and O. J. McConnell, Journal Of Chemical Ecology,1981, Volume 7, Number 6, pages 1115-1133, doi:10.1007/BF00987632
- Ashmore, quoted in McKay and Fowler 1997 b
- McKay and Fowler 1997 b
Further reading 
- Abbott R. T. (1974). American Seashells. Second edition. Van Nostrand Rheinhold, New York
- Abbott R. T. (1986). Seashells of North America, St. Martin's Press, New York
|Wikimedia Commons has media related to: Littorina littorea|
- Littorina littorea (mollusc) from the Invasive Species Specialist Group website of the World Conservation Union
- Common periwinkle from the Marine Life Information Network for Britain and Ireland
- Anatomy of the Periwinkle from a Lander University website