A limpet, 'Opihi (Patella vulgata) is a marine Mollusk of the class Gastropoda. They are somewhat like snails, but have flatened, cone-shaped shells. They live on rocky coasts of most oceans. Limpets can be commonly found attatched to rocks, looking like little disks or bumps on the rock surface. During low tides, they attach themselves using suction to the rocks to protect them from dessication. When the tide returns, limpets lift their shells and continue to graze on Algae found on the rock surfaces, by gathering them into its mouth with a radula, a ribbon-like tongue with rows of teeth. Limpets move by rippling the muscules of their foot in a wave-like motion. Some limpets have a hole at the top, through which gaseous exchange can occur. Most limpets are less than 3 inches (8 cm) long, but a West Mexican Limpet grows to be 8 inches (20 cm).
Limpets return to the same spot just before the tide recedes (presumably due to the shape of their shells growing to match the contours of their ‘patch‘ of rock). It is still unclear how limpets find their way back to the same spot each time, but it is thought that they follow a mucus trail left as they move.