Saltwater snails are the most prolific, having about 55,000 species. They may live from 2 to 20 years. They are found in almost every habitat, be it damp land, fresh water, or sea water. The snail's most defining characteristic is its spiral shell, which is a living part of its body. The shell grows along with the snail, and provides a retreat in times of danger.
Most sea snails have a lid-like part, called an operculum, which serves to close the entrance.
Snails crawl along by a large, muscular foot. As the muscles ripple, a lubricating slime is secreted to help the snail glide over any type of terrain. They can slide over sharp glass and up walls or plants in this way. The snail's head is actually a part of the foot. Most land snails have two pairs of tentacles, whereas aquatic snails generally have just one pair.