Gastropods are one of the most diverse groups of animals, both in form, habit, and habitat. They are by far the largest group of molluscs, with more than 62,000 described living species, and they comprise about 80% of living molluscs. Estimates of total extant species range from 40,000 to over 100,000, but there may be as many as 150,000 species! There are about about 13,000 named genera for both Recent and fossil gastropods. They have a long and rich fossil record from the Early Cambrian that shows periodic extinctions of subclades, followed by diversification of new groups.