What type of animal is classified as an octopus?

An octopus is classified as a mollusk, which is a diverse group of invertebrate animals that includes creatures like snails, clams, and squids. Mollusks are characterized by their soft bodies, which are often protected by a hard shell, although in the case of octopuses, they have evolved to have no external shell. Octopuses belong to the class Cephalopoda within the phylum Mollusca, which means "head-foot," referring to their unique body structure where the head is located above the foot (which is modified into arms and tentacles).

The classification of octopuses under mollusks helps explain several key biological traits they share with other members of this group, such as their soft body structure, the presence of a mantle, and a complex nervous system. Additionally, mollusks are known for their diverse habitats and lifestyles, which can range from aquatic to terrestrial environments.