Gastropod

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Gastropods (; previously known as Univalves; class Gastropoda ) are a vast and diverse group of invertebrates within the phylum Mollusca, comprising the animals commonly known as snails and slugs. With an estimated 65,000 to 80,000 living species, they form the second-largest animal class after the insects. The fossil record of gastropods extends back to the Late Cambrian. As of 2017, 721 families are recognized—476 extant (some with fossil representatives) and 245 extinct known only from fossils. Gastropods inhabit an extraordinary range of environments, including marine, freshwater, and terrestrial ecosystems. They occur in gardens, woodlands, deserts, mountains, rivers, lakes, estuaries, mudflats, intertidal zones, the deep sea, hydrothermal vents, and even in parasitic niches. The term snail generally refers to gastropods with a large external shell into which the body can fully retract, while slugs have no shell or a small internal one, and semislugs can only partially withdraw into...

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