Common Periwinkle (Littorina littorea)
Phylum: Mollusca, Class: Gastropoda, Order: Littorinimorpha, Family: Littorinidae, Genus: Littorina, Species: Littorina littorea · Littorinidae (Periwinkle family) · Gastropod (snail/univalve), whole spiral shell
Species
Littorina littorea
Shell Type
Gastropod (snail/univalve), whole spiral shell
Family
Littorinidae (Periwinkle family)
Size
Approximately 0.75 inches in length, which is average for an adult specimen of this species. Adults typically range from 0.5 to 1.2 inches.
Color & Pattern
The exterior features dark brown to nearly black bands or overall dark pigmentation, with some erosion revealing a lighter whitish calcareous layer near the apex. The surface is smooth with fine growth lines.
Rarity
Very Common, frequently found in large numbers along rocky shores and tide pools.
Habitat
Intertidal zone, primarily found on rocky shores, clinging to rocks, tide pools, and in seaweed beds. It is a marine and brackish water species.
Geographic Range
Native to the northeastern Atlantic coasts of Europe, introduced and now widely established along the northeastern and northwestern coasts of North America.
Description
A small, sturdy, turbinate spiral shell with a pointed apex and a relatively large body whorl. The surface is mostly smooth with subtle growth lines, and the aperture is rounded to oval with a simple, unthickened outer lip.
Key Features
Small, globose to conical shape with a relatively short spire, dark brownish-black coloration, and a smooth exterior texture without prominent ribs or spines.
Collector Value
Low commercial value as they are extremely common, but they are classic staple finds for beginning beachcombers and tide pool enthusiasts. Typically valued at less than a dollar.
Condition Notes
Good condition. The shell is intact with some minor natural wear and whitening at the apex, but the main body whorl retains its dark pigmentation. Collectibility grade: Good.
Interesting Facts
The common periwinkle is an invasive species in North America, having been introduced via ship ballast in the 19th century. They are herbivorous grazers that feed primarily on microalgae and macroalgae, effectively scraping surfaces clean with their radula.
Ecological Role
As abundant herbivores, periwinkles play a crucial role in controlling algal biomass on rocky shores, which in turn affects community structure and competition among marine organisms. They are prey for crabs, shorebirds, and fish.
Similar Species
Rough Periwinkle (Littorina saxatilis) and Smooth Periwinkle (Littorina obtusata). L. obtusata is usually more blunt and brightly colored (yellow/orange/olive), while L. saxatilis is smaller and more heavily sculptured.
Beach Finding Tips
Look along rocky intertidal zones during low tide, particularly on rock faces, crevices, and among fucoid seaweeds where they congregate in large numbers.