The octopus is an invertebrate, which means that the octopus has no bones. It's in the branch of the cephalopodes, which means that the octopus lacks a body, it has only a head and legs (eight of them). It belongs in the order of Octopoda, and there around 300 species. The octopus is one of the largest, fastest, and the most intelligent of all of the invertebrates.
