Class Cephalopoda

Cephalopods are the ocean's ultimate shape shifters with vast cognitive abilities including octopuses, squid, cuttlefish, and nautiluses. Over the course of millions of years, nautiluses have gone virtually unchanged unlike most cephalopods. They have a spiral shell divided into chambers in which they use to control buoyancy and effortlessly float through the ocean, a perfect design in no need of change. While it may seem as if the nautilus is the only animal with a present shell, both the cuttlefish and squid have retained an internal shell for support. Giving the cuttlefish their name, they posses a unique internal cuttlebone made of primarly calcium carbonate. This brittle structure allows the animal to control buoyancy by adjusting how much gas is present in its chambers. In comparison, squid have a structure known as the 'pen', a flexible, internal feature composed of chitin that supports the mantle and provides an anchor for muscle attachment. The octopus is the only cephalopod completing lacking an internal or external shell. As a result, the octopus has great flexibility but must rely on its mantle and hydrostatic pressure for support.

Unlike most mollusks, they have a closed circulatory system, complex nervous, and well-developed eyes giving them advanced eye sight and rapid responses to external stimuli. Cephalopods are among the intelligent animals due to their vast learning and problem-solving as a result of this advanced nervous system and large brains. Many species are able to navigate mazes, camouflage based on external stimuli, adapt to external pressures, and even show evidence of REM/non-REM sleep states.