A dirty-gray eroded shell camouflages this periwinkle on rock faces in the high intertidal and splash zones. Only salt spray and splashes from high waves reach here, forming pools that dry in the sun. Out of reach of the tide, eroded periwinkles live out of the water most of the time.
During dry periods, the periwinkle draws into its shell and closes its operculum (trap door)—this keeps its gills moist, and also keeps fresh water and dry winds out. A periwinkle secretes a mucous glue that holds its shell to its rocky home. Adult eroded periwinkles can survive in this mode for extended dry periods—up to 17 weeks.
The hobby or business of collecting seashells, especially by killing live animals in their shells, causes problems for marine creatures and could seriously affect the population of some species of snails. Even empty shells have a place in the marine environment—many shells provide homes for other animals, like hermit crabs. Instead of collecting snails, it’s best to just look. Without disturbing them, you can photograph snails or make notes of their behavior and habits. Consider sending your observations to a marine biologist—you just might discover a behavior never before seen!
Periwinkles can survive in fresh water—like puddles made by rain—for several days; most marine animals cannot.
A periwinkle, like most molluscs, uses a radula (a rough tongue or band of horny teeth) to scrape diatoms and algae from rocks. The rasping activity of the periwinkle may deepen high tide pools by almost one-half inch (1.25 cm) every 16 years. When a periwinkle population is thriving, it can considerably erode tide pools.
The checkered periwinkle, L. scutula, ranges from Alaska to Baja California. It lives lower down on the rocks than L. planaxis and is not as well adapted for dry periods. Instead, the checkered periwinkle migrates up and down rocks, following the high and low tides.