This is the largest living marine snail, having a shell diameter from 2.25 to 5.5 inches (5.7 to 14 cm). The shell is almost round, large, thick and yellowish-white to pale brown in color. When the fleshy mantle is extended, it will nearly cover the snail’s shell.
Moon Snails glide on a voluminous, heavily ciliated, mucus covered body part called a foot which, when fully extended, can be about 12 inches (30.5 cm) long. The animal can shrink by discharging water, sliding into its shell, and sealing the opening by closing its operculum. The snail cannot stay in the shell for long periods because it cannot breathe. The life expectancy is estimated as several years.
Moon Snails are the predators of clams, mussels, or other mollusks. Sometimes they will even prey on their own species. The foot is used to clamp onto the clamshell and their tongue, a radula, can proceed to drill a hole in the clam’s shell. There are studies that indicate an enzyme secretion of carbonic anhydrate has a softening effect on the shell for easier drilling. The foot can form a siphon which can be pushed through the penetrated shell to extract the food. One of the unique features of this animal is in its reproduction. In late spring and early summer, the egg case of the Lewis Moon Snail can be found. It is a jelly-like matrix composed of sand and mucus as a single gelatinous ribbon forming a sand collar. Inside this sand collar are thousands of eggs sandwiched between the sand-mucus layers. When wet, the collar remains quite rubbery and pliable but becomes brittle when it dries out. The eggs hatch into microscopic butterfly-like larvae and are released when the egg collar disintegrates.
The Lewis’s Moon Snail ranges from Vancouver Island, British Columbia to Baja California on or in the sand and mud in protected bays and intertidal areas to depth of 600 feet (183 m).