Periwinkle (snail)

Periwinkle (snail), common name applied to certain gastropod mollusks found on seashores around the world. Periwinkles are a group of marine snails. Their shells are typically mottled gray, white, and black and taper to a straight-sided or rounded cone with an obtuse point. Periwinkles inhabit the littoral zone, the region between low and high tides. Although they must live near the ocean and spend part of their time underwater, they prefer to be partially exposed to air. Some species are edible.

In most periwinkle species, eggs are laid in a gelatinous mass within the tide zone. The egg mass disintegrates within a few hours into several thousand individual eggs, which float away and soon hatch into tiny larvae. In the rough periwinkle, a species usually found near the high-water mark, the young are hatched and develop a hard shell before they leave the mother.

Like land snails, periwinkles have a horny tonguelike radula within their mouths which is used to scrape algae, diatoms, and organic debris from rocks or other hard surfaces. Periwinkles are considered beneficial because they prevent beds of young oysters from being smothered in detritus. Periwinkles can withstand harsh conditions by tightly covering the opening to their shells with a protective plate, called the operculum. When resting on dry land, they can cement the edges of their shells to the rock substrate with a gluey mucus, thereby avoiding dehydration.

Scientific classification: Periwinkles belong to the family Littorinidae, order Mesogastropoda, class Gastropoda. The common periwinkle is classified as Littorina littorea. The rough periwinkle is classified as Littorina saxatilis.