The mollusks compose the large phylum of invertebrate animals known as the Mollusca. Around 85,000 extinct species of mollusks are recognized. Molluscs are the largest marine phylum, comprising about 23% of all the named marine organisms. Numerous mollusks also live in freshwater and terrestrial habitats They are highly diverse, not just in size and in anatomical structure, but also in other factors like behavior and habitat. The phylum is typically divided into 9 or 10 taxonomic classes, of which two are entirely extinct.