Cephalopods are a class of mollusks that include octopuses, squids, cuttlefish, and nautiluses. They are characterized by their distinct head, large eyes, and tentacles, which are equipped with suckers or hooks. Known for their advanced nervous systems and behaviors, cephalopods are also capable of complex camouflage and rapid movement in the water. They are primarily found in marine environments and play significant roles in ocean ecosystems.