The squid and the octopus are different animals, although they both belong to the molluscan class Cephalopoda and, as such, are related. One major difference between the squid and the octopus is the number of arms. Squid have 10 arms compared to the eight of the octopus.
Approximately 800 living species of cephalopod exist and are found in all oceans. Their range of depth varies by species, with some preferring to hunt near the ocean's surface and others living in the abyssal plane. Having a highly developed nervous system, cephalopods are some of the most intelligent invertebrates on the planet.