Cephalopoda (class)

A class of highly advanced and organized, exclusively marine animals having a well-developed head with large, well-organized eyes, a pair of strong, bony jaws like a parrot's beak, a set of elongated muscular arms or tentacles usually furnished with prehensile suckers or hooks, and in most species a bag of inklike fluid which they can eject to foil predators. Familiar representatives are the octopus, squid, cuttlefish, and chambered nautilus; there were a large number of distinct extinct forms, particularly flourishing in the late Paleozoic and Mesozoic times.