Octopuses

Octopuses are cephalopod mollusks, related to squid, cuttlefish and nautiluses. The group is recognized by its eight arms, which bear suckers and serve both for movement and for handling objects. Unlike squid and cuttlefish, octopuses do not have a separate pair of long feeding tentacles. Most have a soft body without an external shell; a hard, beak-like mouth is among the few rigid structures. The mantle encloses the main organs, while a funnel, or siphon, helps move water through the body and can also be used in propulsion. Species differ greatly in size, shape and habitat, so a description of one octopus should not be assumed to fit them all.

Octopus species live in every ocean, from shallow coastal waters to deep-sea habitats. Many spend much of their time on or near the seafloor, often using crevices or other sheltered places as dens; habits vary among species. Octopuses are predators. Their prey commonly includes crabs, shrimp, clams and other mollusks, though diets differ with habitat and body size. Suckers give the arms a strong grip and provide touch and chemical information, helping an octopus investigate surfaces and manipulate food. The beak cuts prey into manageable pieces before it is swallowed.

Many octopuses are capable of rapidly altering the color and appearance of their skin. Pigment cells and other skin structures help create patterns that can make an animal less visible against a background or produce a conspicuous display. Some species also alter skin texture or posture, changing the outline of the body. When a quick escape is needed, an octopus can force water through its siphon and move in the opposite direction. Many can release ink, which can obscure or distract a predator. These strategies are not identical across the group, and camouflage is only one part of octopus behavior.

An octopus has a central brain and a large amount of nervous tissue distributed through its arms. The arms can carry out some sensory and motor actions locally, while the brain also guides goal-directed and coordinated behavior. This arrangement is not equivalent to eight independent brains: research describes connections among the arms and with the central nervous system, and many details of how control is organized remain under study. Experiments have shown octopuses learning tasks, solving some problems and manipulating objects. Such abilities make them notable among invertebrates, but scientists study their cognition on its own terms rather than treating it as a smaller version of human intelligence.