Cephalopod

Cephalopoda; Temporal range:
	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
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Mollusca
Subphylum:	Conchifera
Class:	Cephalopoda; Cuvier, 1797
Subclasses
	Nautiloidea sensu lato (paraphyletic) Plectronoceratoidea † (paraphyletic); Multiceratoidea † (paraphyletic?); Nautiloidea sensu stricto; Endoceratoidea †; Orthoceratoidea † (paraphyletic); ; Bactritoidea † (paraphyletic); Ammonoidea †; Coleoidea; ?Paracoleoidea † (disputed);

A cephalopod /ˈsɛfələpɒd/ is any member of the molluscan class Cephalopoda /sɛfəˈlɒpədə/ (Greek plural κεφαλόποδες, kephalópodes; "head-feet")^[3] 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 to the 14 m (45.1 ft) colossal squid, the largest extant invertebrate.

^ 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
^ Hildenbrand, Anne; Austermann, Gregor; Fuchs, Dirk; Bengtson, Peter; Stinnesbeck, Wolfgang (2021). "A potential cephalopod from the early Cambrian of eastern Newfoundland, Canada". Communications Biology. 4 (1): 388. doi:10.1038/s42003-021-01885-w. PMC 7987959. PMID 33758350.
^ 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.

[mollusca11-1] 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

[ReferenceD-2] Hildenbrand, Anne; Austermann, Gregor; Fuchs, Dirk; Bengtson, Peter; Stinnesbeck, Wolfgang (2021). "A potential cephalopod from the early Cambrian of eastern Newfoundland, Canada". Communications Biology. 4 (1): 388. doi:10.1038/s42003-021-01885-w. PMC 7987959. PMID 33758350.

[3] 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.

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