|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.
While climbing, exposed to either extreme cold or heat, they hide in the shells and start rolling, hopefully hitting the water. 
Measuring the shell from the end of the aperture to the apex reveals the length of the snail. Turning the shell over with the aperture flat on a surface and measuring vertically reveals the height of the snail. These measurements can be done using a caliper.
Common periwinkles are native to the North-eastern coasts of the Atlantic Ocean, including northern Spain, France, England, Scotland, Ireland, Scandinavia, and Russia.
There have been more than 14 000 observations made available as a dataset at the Global Biodiversity Information Facility - Littorina Littorea, which can be explored. More distribution information can also be found at Ocean Biographic Information System - Littorina Littorea. The NBN Gateway - Littorina Littorea have a good distribution map over the UK and Ireland. The datasets may be overlapping.
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. It is primarily an 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.
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 pelagic larvae escape and eventually 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 ten years.
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, England, Wales and Ireland, where they are commonly referred to as winkles or in some areas buckies, willicks, or wilks. In Belgium, they are commonly called kreukels or caracoles. 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.
Following their history as an ancient food source in Atlantic Europe, they are harvested and consumed in the Azores Islands by the Portuguese people, usually called búzios, the generic name for sea snails.
Similar foods are consumed by other maritime cultures throughout the world, such as the Chinese people. Periwinkles, or a similar species, are sold at the live seafood counter in the Chinese-Canadian grocery chain, T&T Supermarket.
Periwinkles are graded by number of snails per kilogram. The following table displays some common grades in France, and the value they commonly fetch from the primary producer. The actual value is depending upon supply and demand, with seasonal variations. The actual ranges may also differ from each establishment.
|Grade name||Number per kilogram||Common value EUR/kg|
The method used for grading differs, but two proven methods include a Trommel screen with horizontal bars instead of a mesh, and a Circle-throw vibrating machine also using bars. The price to purchase a complete sorting machine can be 10 000 EUR and upwards.
After grading, the periwinkles are "climbed" close to the end consumer, a term used to describe the act of checking if they are still alive. This can take anywhere from a few hours to several days, depending on how virile the periwinkles are, and the temperature of the water they climb in. Any periwinkles left immobile at the bottom are considered dead, and is waste. It is not uncommon to have up to 8% waste in a shipment.
Hereafter, the winkles are commonly packed in smaller quantities, before being distributed to customers. Mesh bags from 3 to 10 kg are common.
The Common Periwinkle is sold by fishmongers at seafood markets in large cities around the world. One such market is Marché_international_de_Rungis in Paris. Most of the volume is consumed by France, Belgium, Spain and the Netherlands.
Methods to increase commercial value
Ongrowing has been investigated as a potential way of increasing commercial value, but no documented pilot facilities have been established. By harvesting the periwinkle during the summer, and storing them with feed until December, not only should the grade have been increased, but the market value should be higher since supply is lower in the cold winter months. 
- 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 20.04.2016
- 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.
- Eschweiler, N., Molis, M. & Buschbaum, C. Helgol Mar Res (2009) "Habitat-specific size structure variations in periwinkle populations (Littorina littorea) caused by biotic factors" doi:10.1007/s10152-008-0131-x
- 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
- 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
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