The octopus belongs to the phylum Mollusca in the Animalia kingdom. The phylum contains a large number of aquatic life forms in addition to the octopus, such as squid, mussels and oysters.
The phylum Mollusca is the second largest animal phylum and contains seven classes. According to Bioweb, the phylum contains more than 75,000 different species, which live in both freshwater and saltwater as well as on land. Features of the phylum include a soft body and an elongated head. While most members of this phylum have a shell to protect the soft body, the octopus belongs to the more predatory class Cephalopoda, along with similar animals such as squid.