Cephalopod

Cephalopods are a class of marine molluscs that includes octopuses, squid, cuttlefish, and nautiluses.

Cephalopods are a class of marine molluscs that includes octopuses, squid, cuttlefish, and nautiluses. They are known for their advanced nervous systems, arms or tentacles, and diverse body forms, with most living species belonging to the coleoids. The group is entirely marine and has a long fossil record that includes many extinct forms.

Classification and anatomy

Cephalopods are molluscs with bilateral symmetry, a prominent head, and arms or tentacles surrounding the mouth. Their body plan is distinct from other molluscs and is associated with highly developed sensory and nervous systems.

Major living groups

Living cephalopods are commonly divided into the Coleoidea, which includes octopuses, squid, and cuttlefish, and the Nautiloidea, represented today by nautiluses. In coleoids, the shell is reduced, internal, or absent, while nautiluses retain an external shell.

Behaviour and adaptations

Many cephalopods can change colour, swim by jet propulsion, and use arms or tentacles to capture prey. They are active marine predators, and their eyes and nervous systems are often compared with those of vertebrates.

Evolution and fossils

Cephalopods have a long evolutionary history and were especially diverse in the late Paleozoic and Mesozoic eras. Extinct groups such as ammonites and belemnites are important parts of their fossil record.