Snails are neither mammals nor reptiles. They belong to the phylum Mollusca and are classified as gastropods. Gastropods are characterized as having a single shell that is capable of hiding them completely.
Other characteristics of gastropods include a complete digestive track and one large "foot" that is responsible for all movement. Many also contain what is known as a radula, which is a special organ made of chitin inside the animal's mouth. This organ evolved to allow the gastropod to scrape food from whichever surface it moves across. Gastropods are one of the most diverse classes of animals on the planet, second only to insects, and contain the only species of mollusk that can live on land.