The molluscs compose the large phylum of invertebrate animals. Around 85,000 species of mollusks are recognized. Molluscs are the largest marine phylum, comprising about 25% of all marine organisms. Mollusks also live in freshwater and on land. They are highly diverse, not only in size and in structure, but also in behavior and in habitat. The phylum is typically divided into 9 or 10 classes. Cephalopod mollusks, such as squid, cuttlefish and octopus, are among the smartest of all invertebrates—and either the giant squid or the colossal squid is the largest known invertebrae. The gastropods (snails and slugs) are by far the most numerous mollusks.