Gastropods are snails and slugs. The name gastropod, which means "stomach foot," refers to the fact that most slugs and snails crawl around on their stomach (ventral) side. Snails are molluscan animals that commonly have coiled shells. Some snails have a second, smaller shell called an operculum, that acts as a door to protect the snail from predators or from drying out. Slugs do not have shells and so are not found as fossils.