The soft body of a snail is usually protected by a shell. The animal crawls along on a muscular organ called a foot. The muscles in the foot move backwards in a wave-like action. This action moves the snail forwards. Snails have a head with tentacles, or feelers, eyes, a mouth and tiny teeth. All land snails breathe through lungs. Most water-living snails breathe through gills, like fish. Some have lungs and must come to the surface of the water to breathe. The smallest snail is no larger than a pin-head. The largest can grow to 77 centimeters long!