A cuttlefish is a type of mollusk, a Cephalopod, which has a highly developed central nervous system. Similar to octopus and squid, they are arguably among the smartest invertebrates with the largest brain-to-body size ratio of all invertebrates. They have an internal shell called a cuttlebone, which is porous and filled with gas, allowing the animal to maintain buoyancy. They have a typical life expectancy of one to two years.
Cuttlefish are remarkable for their ability to change color at will, using a set of specialized, pigmented skin cells called chromatophores and nerve cells, which interact to expand and contract, exposing various pigments as needed. This color change is useful for camouflage, communication between each other, and as a warning to predators.