A snail is a type of animal that belongs to the phylum Mollusca and the class Gastropoda. Gastropods are a major part of the phylum Mollusca and are the most highly diversified class in the phylum, with 65,000 to 80,000 living snail and slug species. Snails are easily identifiable by their spiral shell, which they retract into when threatened. They are found almost everywhere in the world, from high mountains to simple botanical gardens to deep undersea rocks. Snails have considerable human relevance, including as food items, as pests, and as vectors of disease, and their shells are used as decorative objects and are incorporated into jewelry.