Checkered Periwinkle (Littorina scutulata)
This small (up to 1.5 cm long), sharply pointed snail is abundant on rocks in the high intertidal zone of Puget Sound. The coloration of the shell is quite varied, from mostly dark, with a variable checkered white pattern, to mostly pale with dark spiral bands, themselves sometimes checkered with paler markings. The shell is smooth, with little or no sculpturing.
Periwinkles are herbivores, scraping soft-bodied algae from the rocks with their radula; tiny animals living on the algae may also be ingested. As food is abundant for them, the snails can be abundant as well, sometimes in masses on an exposed rock surface. Because they live high in their zone, they are often exposed to the air, and they can close their shell tightly with the horny operculum attached to their foot to keep water inside and to avoid both desiccation and suffocation.
Unlike most marine organisms, periwinkles spend much of their time out of the water. They feed not only on algae and diatoms but also on lichens above the high-tide line. They usually crawl out of the water at night, when conditions are less adverse to a marine animal out of its environment. That is, it is cooler and moister at night. They may be especially active on foggy nights.
Checkered Periwinkles are slow-growing but are known to live as long as seven years. They have a wide spectrum of predators, from fish and six-armed sea stars to gulls and scoters. Obviously only certain predators have access to an animal species that lives in a restricted tidal zone.
Breeding takes place from spring to fall, peaking in midsummer; egg laying is at night. The eggs are laid in flattened frisbee-shaped capsules, and they float freely in the water. Each capsule holds about three eggs, and a female can lay 1000 capsules in a week. The eggs hatch into veliger larvae, which travel in the plankton until they undergo metamorphosis in a month or two and settle on the rocks again. Some periwinkle species do not have planktonic larvae, and their dispersal ability is thus more limited.