Common Periwinkle (Littorina littorea)
Alternate common names: Periwinkle, Winkle.
Color: Shell is dark in color, usually brown, black, or gray.
Size: 1 inch long and 3/4 inch wide.
Habitat: Intertidal zones, rocky shores, tide pools, pilings, and rock jetties.
Seasonal appearance: All year.
The common periwinkle, related to limpets, whelks, and other marine snails, is the most common snail in Rhode Island. A single spiral shell that grows with their bodies protects these small snails. The body includes a fleshy foot, a short tail, and two antennae on the head. The cream-colored foot of the common periwinkle is divided into a right and a left half, which the snail moves alternately as the muscle ripples forward. Their stalked tentacles are sensory organs that are used to see and taste.
Life History and Behavior
Common periwinkles use their foot to hold securely onto rocks when waves crash over them or marsh grasses when the tide rises. They are closely related to the marsh periwinkle (Littorina irrorata), which is more common in salt marshes. Common periwinkles are herbivores, using their file-like tongue, the radula, to feed on diatoms and algae attached to intertidal rocks. The common periwinkle breaks down its food by mixing it with mucous on the radula before bringing the food into its mouth. Sea stars, whelks, and some fish eat common periwinkles. The shells of dead common periwinkles are often inhabited by hermit crabs.
Common periwinkles can live for many days without food or water by retaining moisture in their gills. They close themselves into their shells and excrete a sticky mucous that hardens, firmly attaching the animal to the rock or blade of seagrass. They are able to adapt to a variety of environmental conditions, including extreme heat and wind, low tide, severe wave action, and submergence at high tide.
Adapted from The Uncommon Guide to Common Life on Narragansett Bay. Save The Bay, 1998.