page_title: Cephalopod
section_title: Taxonomy
hierarchical_section_title: Cephalopod / Evolution / Taxonomy
caption_attribution_description: Sepia officinalis&#160;Linnaeus, 1758 English: Cuttlefish at Nausicaä Centre National de la Mer, Boulogne-sur-Mer, France
context_page_description: A cephalopod is any member of the molluscan class Cephalopoda 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 modified from the primitive molluscan foot. Fishermen 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 and Belemnoidea.
context_section_description: The classification presented here, for recent cephalopods, follows largely from Current Classification of Recent Cephalopoda (May 2001), for fossil cephalopods takes from Arkell et al. 1957, Teichert and Moore 1964, Teichert 1988, and others.  The three subclasses are traditional, corresponding to the three orders of cephalopods recognized by Bather.
  Class Cephalopoda († indicates extinct groups)
  Subclass Nautiloidea: Fundamental  ectocochliate cephalopods that provided the source for the Ammonoidea and Coleoidea.
  Order † Plectronocerida: the ancestral cephalopods from the Cambrian Period
  Order † Ellesmerocerida (500 to 470 Ma)
  Order † Endocerida (485 to 430 Ma)
  Order † Actinocerida (480 to 312 Ma)
  Order † Discosorida (482 to 392 Ma)
  Order † Pseudorthocerida (432 to 272 Ma)
  Order † Tarphycerida (485 to 386 Ma)
  Order † Oncocerida (478.5 to 324 Ma)
  Order Nautilida (extant; 410.5 Ma to present)
  Order † Orthocerida (482.5 to 211.5 Ma)
  Order † Ascocerida (478 to 412 Ma)
  Order † Bactritida (418.1 to 260.5 Ma)
  Subclass † Ammonoidea: Ammonites (479 to 66 Ma)
  Order † Goniatitida (388.5 to 252 Ma)
  Order † Ceratitida (254 to 200 Ma)
  Order † Ammonitida (215 to 66 Ma)
  Subclass Coleoidea (410.0 Ma-Rec)
  Cohort † Belemnoidea: Belemnites and kin
  Genus † Jeletzkya
  Order † Aulacocerida (265 to 183 Ma)
  Order † Phragmoteuthida (189.6 to 183 Ma)
  Order † Hematitida (339.4 to 318.1 Ma)
  Order † Belemnitida (339.4 to 66 Ma)
  Genus † Belemnoteuthis (189.6 to 183 Ma)
  Cohort Neocoleoidea
  Superorder Decapodiformes (also known as Decabrachia or Decembranchiata)
  Order Spirulida: Ram's horn squid
  Order Sepiida: cuttlefish
  Order Sepiolida: pygmy, bobtail and bottletail squid
  Order Teuthida: squid
  Superorder Octopodiformes (also known as Vampyropoda)
  Family † Trachyteuthididae
  Order Vampyromorphida: Vampire squid
  Order Octopoda: octopus
  Superorder † Palaeoteuthomorpha
  Order † Boletzkyida
  Other classifications differ, primarily in how the various decapod orders are related, and whether they should be orders or families.
caption: Common cuttlefish (Sepia officinalis)
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