ABSTRACT
Cephalopods include the living coleoids, and some coleoids including the belemnites. Living cephalopods represent a considerable amount of biomass in the oceans and are an important constituent of the marine fishery catch. Living cephalopods include both active swimmers and bottom dwellers. Many pelagic species of squid have very streamlined bodies for efficient locomotion. Cephalopods are well represented in the fossil record, with around 11,000 extinct species described. The interior of all calcareous cephalopod shells is chambered. In externally shelled cephalopods, the body of the animal is contained within the last, open section of the shell while the chambers are utilised as a buoyancy device. All cephalopods are carnivorous, while fish have a wide range of diets, including some being predators. Both have adaptations to control buoyancy, although the mechanisms are different. Nautiliform cephalopods first appeared in the Furongian and underwent a rapid diversification in the Ordovician.
