cephalopod

Cephalopods are a class of marine mollusks that includes octopuses, squids, cuttlefish, and nautiluses. They are characterized by a prominent head, a body plan with arms or tentacles, a mantle enclosing the internal organs, and a foot modified into a funnel or siphon used for jet propulsion. They typically possess highly developed eyes and a complex nervous system, enabling rapid responses to their environment.

Cephalopods are active predators with beak-like jaws and a radula. Many species display chromatophores and other pigment cells that allow rapid color and texture changes for camouflage and signaling. An ink sac provides a defensive spray, and several species can produce a defensive mantle flare or jet escape. Gills handle respiration, and most possess a closed circulatory system.

They occupy diverse marine environments from shallow reefs to deep oceans. They are mainly carnivorous, feeding on fish, crustaceans, and mollusks. Locomotion combines jet propulsion with fin movement and, in some species, arm-based crawling. Reproduction is generally sexual; males transfer spermatophores to females, eggs are laid and commonly guarded until hatching. Lifespans vary, with many smaller species short-lived, while nautiluses can live longer and reproduce more slowly.

The class comprises octopuses, squid, cuttlefish, and nautiluses. The fossil record dates to the Cambrian era, including now-extinct groups such as ammonites. Cephalopods are important model organisms in neuroscience and biomechanics, and they contribute to human food supplies. Conservation concerns include overfishing and habitat degradation.