ABSTRACT
Cephalopod is a mollusk class that separated from their ancestors, probably about 200 million years ago. Cephalopods include chambered nautiluses, with external shells and anatomy that has remained virtually unchanged for 450 million years, and soft-bodied coleoids: Decapod and Octopoda. Coleoids are agile predators, equipped with highly efficient and flexible arms capable of a wide range of movements with no skeletal support, allowing them to face and find solutions to different environmental challenges. The generalization that cephalopods are solitary outside of the reproductive period would be true, with small exceptions and some variation. The females join in this swim in circles which initially can seem very strange and out of control, but after a while squids start to swim in pairs. Octopuses are mollusks that have completely lost their shell, although one species, the Argonaut, create a paper-thin replica of the nautilus shell from one of its arms, and uses it as the receptacle for its eggs.
