# Common Periwinkle (*littorina littorea*) The Common Periwinkle (Littorina littorea) is a small but mighty marine gastropod that dominates the rocky shores of the North Atlantic. Known for its incredible resilience, this robust sea snail is a master of the intertidal zone, enduring pounding waves, fluctuating temperatures, and prolonged exposure to air during low tide. Native to Europe but now widespread along the North American coastline as an introduced species, it plays a massive role in shaping coastal ecosystems through its constant grazing on algae. Beyond its ecological significance, the Common Periwinkle has a long history intertwined with human culture. It has been gathered as a nutritious coastal food source for thousands of years, commonly boiled and eaten as a traditional seaside snack. Whether you are turning over rocks in a tidal pool or admiring the biodiversity of a rugged shoreline, you are almost guaranteed to cross paths with this hardy, ubiquitous little mollusk. - **Category:** [Invertebrate](https://www.snappit.app/explore/categories/invertebrate) - **Rarity:** Common - **Danger:** 1/5 · Very low - **Snaps:** 7 - **Habitat:** Found along rocky coastlines, often clinging to rocks, tide pools, and seaweed in the intertidal zone. ![Common Periwinkle](https://inaturalist-open-data.s3.amazonaws.com/photos/183802255/medium.jpeg) Photo: Jessica Utrup, CC BY 4.0 · [iNaturalist](https://www.inaturalist.org/photos/183802255) ## Appearance The Common Periwinkle features a thick, robust, spiral shell that typically measures between 1 to 3 centimeters in height. The shell has five to six slightly convex whorls, tapering to a sharply pointed apex. Its coloration is generally dark, ranging from grey-black to dark brown, though it can occasionally exhibit lighter spiral banding or a reddish tint. The opening of the shell is ovate with a pale inner lip. When active, its fleshy, dark-grey body and two sensory tentacles emerge. When threatened or exposed to air, the snail retreats and seals the opening with a dark, corneous 'trapdoor' known as an operculum. ## Taxonomy - **Kingdom:** Animalia - **Phylum:** Mollusca - **Class:** Gastropoda - **Order:** Littorinimorpha - **Family:** Littorinidae - **Genus:** Littorina ## Interesting facts - Common Periwinkles were introduced to North America in the mid-19th century and have since become one of the most abundant shoreside snails there. - In the UK, eating boiled winkles using a pin to extract the snail from its shell is a traditional seaside activity dating back centuries. - Their constant grazing uses a radula covered in microscopic teeth that actually erodes coastal rocks over long periods of geological time. - To survive low tide on hot days, they can produce a specialized glue that attaches their shell lip to a rock, hanging freely to avoid absorbing excess heat from the stone. ## Special abilities - **Desiccation Resistance:** It can seal its shell tightly with a horny trapdoor called an operculum, allowing it to survive for weeks out of water without drying out. - **Radula Scraping:** Equipped with a ribbon of microscopic, chitinous teeth known as a radula, it efficiently scrapes tough algae and diatoms directly off hard rock surfaces. - **Wave Adhesion:** It secretes a powerful mucus foot-hold that allows it to grip slick, wave-battered rocks, preventing it from being washed out to sea during storms. ## Measurements & details - **Length:** 1-3 cm - **Weight:** 0.002-0.015 kg - **Lifespan:** 3-10 years - **Clutch Size:** 10000-100000 - **Incubation:** 5-6 days ## Diet & Feeding The Common Periwinkle is primarily a grazing herbivore, feeding on microalgae and the germlings of larger seaweeds. - **Age differences:** Larvae are pelagic and feed on phytoplankton before settling on rocks to graze on benthic algae as adults. - **Primary Foods:** Diatoms, Microalgae, Green algae, Brown seaweed detritus - **Foraging Method:** Grazing ## Ecological connections - **Eaten by:** [European Green Crab](https://www.snappit.app/explore/european-green-crab) (*Carcinus maenas*) — A common predator that actively crushes and eats periwinkles. - **Eaten by:** [Herring Gull](https://www.snappit.app/explore/herring-gull) (*Larus argentatus*) — Birds that forage in the intertidal zone will swallow periwinkles whole or drop them on hard rocks to break their shells. - **Host plant:** [Knotted Wrack](https://www.snappit.app/explore/knotted-wrack) (*Ascophyllum nodosum*) — Provides a resting place and a source of epiphytic algae for the periwinkle to graze upon. ## Safety **Danger:** 1/5 · Very low No special safety notes yet. ## Frequently Asked Questions ### How to identify Common Periwinkle? Compare the overall shape, opening, spiral, ribs, hinge and surface sculpture. Beach shells often lose the colors and sharp edges they had on the living animal, so shape does most of the work. Seashell Identifier: upload a photo and compare the visible details. ### How long is Common Periwinkle? 1-3 cm ### How much does Common Periwinkle weigh? 0.002-0.015 kg ### How long does Common Periwinkle live? 3-10 years ### What does Common Periwinkle eat? The Common Periwinkle is primarily a grazing herbivore, feeding on microalgae and the germlings of larger seaweeds. ### Where is Common Periwinkle usually found? Found along rocky coastlines, often clinging to rocks, tide pools, and seaweed in the intertidal zone. ### How does Common Periwinkle hunt? Grazing ### How many eggs does Common Periwinkle lay? 10000-100000 ## Where to spot - [Chestnut Street District](https://www.snappit.app/guides/places/chestnut-street-district) — Massachusetts, US · Historic District - [Fort Revere Park](https://www.snappit.app/guides/places/fort-revere-park) — US · State Park - [Harkness Memorial State Park](https://www.snappit.app/guides/places/harkness-memorial-state-park) — Connecticut, US · Botanical Garden - [Kennebunkport Historic District](https://www.snappit.app/guides/places/kennebunkport-historic-district) — Maine, US · Historic District - [Blithewold Mansion, Gardens and Arboretum](https://www.snappit.app/guides/places/blithewold-mansion-gardens-and-arboretum) — Rhode Island, US · Botanical Garden - [Cape Arundel Summer Colony Historic District](https://www.snappit.app/guides/places/cape-arundel-summer-colony-historic-district) — US · Historic District [View all places to see Common Periwinkle](https://www.snappit.app/guides/where-to-see/common-periwinkle) ## More Invertebrate - [Coral](https://www.snappit.app/explore/coral) - [Crab Spider](https://www.snappit.app/explore/crab-spider) (*Mecaphesa asperata*) - [Garden Spider](https://www.snappit.app/explore/garden-spider) (*Araneus diadematus*) - [Brown Recluse Spider](https://www.snappit.app/explore/brown-recluse-spider) (*Loxosceles reclusa*) --- Source: [Common Periwinkle: Facts & Places to See — Snappit](https://www.snappit.app/explore/common-periwinkle)