Snails, slugs and their relatives are the most common form of mollusc, with over 60,000 species alive today. Most species possess a shell, and the shells of many gastropods have very beautiful patterns and shapes. Sea-living snails and slugs typically start life as a tiny larva floating in the plankton, and only later metamorphose into a crawling creature. On land and in freshwater, however, miniature versions of the adults usually hatch from eggs.
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