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| Cephalopoda Temporal range: Late Cambrian – present;[1]
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| Extant and extinct cephalopods; clockwise from top-left: common octopus (Octopus vulgaris), Caribbean reef squid (Sepioteuthis sepioidea), chambered nautilus (Nautilus pompilius), Orthosphynctes, Clarkeiteuthis conocauda, and common cuttlefish (Sepia officinalis) | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Subphylum: | Conchifera |
| Class: | Cephalopoda Cuvier, 1797 |
| Subclasses | |
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A cephalopod /ˈsɛfələpɒd/ is any member of the molluscan class Cephalopoda /sɛfəˈlɒpədə/ (Greek plural κεφαλόποδες, kephalópodes; "head-feet")[2] such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles (muscular hydrostats) modified from the primitive molluscan foot. Fishers sometimes call cephalopods "inkfish", referring to their common ability to squirt ink. The study of cephalopods is a branch of malacology known as teuthology.
Cephalopods became dominant during the Ordovician period, represented by primitive nautiloids. The class now contains two, only distantly related, extant subclasses: Coleoidea, which includes octopuses, squid, and cuttlefish; and Nautiloidea, represented by Nautilus and Allonautilus. In the Coleoidea, the molluscan shell has been internalized or is absent, whereas in the Nautiloidea, the external shell remains. About 800 living species of cephalopods have been identified. Two important extinct taxa are the Ammonoidea (ammonites) and Belemnoidea (belemnites). Extant cephalopods range in size from the 10 mm (0.3 in) Idiosepius thailandicus[3] to the 700 kilograms (1,500 lb) heavy Colossal squid, the largest extant invertebrate.[4][5]
- ^ Wilbur, Karl M.; Trueman, E.R.; Clarke, M.R., eds. (1985), The Mollusca, vol. 11. Form and Function, New York: Academic Press, ISBN 0-12-728702-7
- ^ Queiroz, K.; Cantino, P. D.; Gauthier, J. A. (2020). Phylonyms: A Companion to the PhyloCode. CRC Press. p. 1843. ISBN 978-1-138-33293-5.
- ^ Okutani, T. 1995. Cuttlefish and squids of the world in color. Publication for the 30th anniversary of the foundation of the National Cooperative Association of Squid Processors.
- ^ McClain, Craig R.; Balk, Meghan A.; Benfield, Mark C.; Branch, Trevor A.; Chen, Catherine; Cosgrove, James; Dove, Alistair D.M.; Gaskins, Leo; Helm, Rebecca R.; Hochberg, Frederick G.; Lee, Frank B.; Marshall, Andrea; McMurray, Steven E.; Schanche, Caroline; Stone, Shane N. (2015-01-13). "Sizing ocean giants: patterns of intraspecific size variation in marine megafauna". PeerJ. 3: e715. doi:10.7717/peerj.715. ISSN 2167-8359. PMC 4304853.
- ^ [Te Papa] (2019). The beak of the colossal squid. Museum of New Zealand Te Papa Tongarewa.