PERIWINKLE

in zoology, any small marine snail belonging to the family Littorinidae. Periwinkles are widely distributed shore (littoral) snails, chiefly herbivorous, usually found on rocks, stones, or pilings between high- and low-tide marks; a few are found on mud flats, and some tropical forms are found on the prop roots or mangrove trees. Of the approximately 80 species in the world, 10 are known from the western Atlantic. The common periwinkle, Littorina littorea, is the largest, most common and widespread of the northern species. It may reach a length of 4 centimetres (1 1/2 inches), is usually dark gray, and has a solid spiral (turbinate) shell that readily withstands the buffeting of waves. Widespread along the rocky shores of northern Europe, the common periwinkle was introduced into North America at Halifax, Nova Scotia, in about 1857 and has spread as far south as Maryland. It is very common on the rocky shores of New England and also occurs on shallow muddy bottoms, along the banks of tidal estuaries, and among the roots and blades of marsh grass where the water is only moderately salty. The breeding habits of periwinkles are quite variable. Littorina saxatilis, which lives high up on rocks and is often out of water for long periods of time, holds its eggs in a brood sac until the young are fully developed, at which time they emerge as tiny crawling replicas of the adult. All species in the Littorinidae are important as a favourite food of many shore birds, particulary ducks. Certain other marine snails, such as the common northern lacuna (Lacuna vincta), are sometimes called periwinkles. In many sections of the southern United States, the term periwinkle, or pennywinkle, is applied to any small freshwater snail. in botany, any of various plants of the genus Vinca of the dogbane family (Apocynaceae). The name periwinkle is possibly taken from pervinka, the Russian name of the flower, which in turn is derived from pervi, "first," as it is one of the first flowers of spring. The lesser periwinkle (V. Minor), with lilac-blue flowers, 2 centimetres (3/4 inch) across, an evergreen, trailing perennial, is native to Europe and is found in the British Isles. Introduced into North America, it is now widespread over much of the eastern continent. The similar greater periwinkle (V. major), with purplish-blue flowers, 2 1/2 to 5 cm across, native to continental Europe, has become naturalized in England.