Cephalopoda

Article By:

Voight, Janet R. Department of Zoology, Field Museum, Chicago, Illinois.

Roper, Clyde F. E. Division of Molluscs, Smithsonian Institution, U.S. National Museum, Washington, DC.

Ward, Peter D. Department of Geological Sciences, University of Washington, Seattle, Washington.

Last reviewed:July 2021

DOI:https://doi.org/10.1036/1097-8542.120800

A class in the phylum Mollusca that is exclusively marine and includes squids, octopuses, and cuttlefishes. The molluscan class Cephalopoda is one of the major taxonomic groupings of marine animals and contains both extant members—squids (Fig. 1), cuttlefishes, octopuses, and chambered nautiluses—and fossil taxa—ammonoids, belemnoids, and nautiloids. The earliest known cephalopod fossils date to roughly 500 million years ago from the Upper Cambrian of northeast China. Fossilized external shells of members of the extinct subclass Ammonoidea and the nearly extinct subclass Nautiloidea are interpreted as indicating that these animals were shallow-living and slow-moving. Despite the thousands of species of such shelled cephalopods that have been recognized in the Ammonoidea and Nautiloidea, all are extinct, except for six species in two surviving genera, Nautilus and Allonautilus. Other living cephalopods—all predators in the subclass Coleoidea with internal shells—number more than 800 species. See also: Ammonoidea; Belemnitida; Coleoidea; Mollusca; Nautiloidea

The content above is only an excerpt.