Common Periwinkle

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 varies 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 is chocolate brown.

The width of the shell ranges from 10 to 12 millimetres (3⁄8 to 1⁄2 in) at maturity, with an average length of 16 to 38 mm (5⁄8 to 1+1⁄2 in). Shell height can reach up to 30 to 52 mm (1+1⁄8 to 2 in), The length is measured from the end of the aperture to the apex. The height is measured by placing the shell with the aperture flat on a surface and measuring vertically.

Common periwinkles are native to the northeastern coasts of the Atlantic Ocean, including northern Spain, France, Great Britain, 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 has a distribution map over the UK and Ireland. These datasets may overlap.

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. It uses its radula to scrape algae from rocks and, in the salt marsh community, pick up algae from cord grass or from the biofilm that covers the surface of mud in estuaries or bays. Macroalgae that are readily consumed include Ulva lactuca and Ulva intestinalis; if provided, blue mussel can also be eaten.

The radula is taenioglossate, consisting of seven teeth per row: one middle tooth, flanked on each side by one lateral and two marginal teeth. The radula is used to scrape algae and detritus.

Phlorotannins in the brown algae Fucus vesiculosus and Ascophyllum nodosum act as chemical defenses against L. littorea.

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 55 metres (180 ft). When exposed to either extreme cold or heat while climbing, a periwinkle will withdraw into its shell and start rolling, which may allow it to fall to the water.

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. Benson suggests that it reaches maturity at 10 mm and normally lives five to ten years. while Moore suggests that maturity is reached in 18 months. Some specimens have lived 20 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 B.C.E. in Scotland. It is still collected in quantity in Scotland, mostly for export to the Continent and also for local consumption. 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.