Coleoidea

(invertebrate zoology) A subclass of cephalopod mollusks including all cephalopods except Nautilus, according to certain systems of classification.

A subclass of the Cephalopoda that appeared in the middle Paleozoic (Early Devonian Period) and presumably evolved from the nautiloid stalk. Of the five orders of fossil coleoids, the belemnites are conspicuous with their fossilized shells termed lightning bolts. All these forms became extinct by the end of the Mesozoic, 65 million years ago. The surviving four orders that developed in the Late Triassic to Late Cretaceous represent all the living cephalopods today, except Nautilus (subclass Nautiloidea).

Coleoids are characterized by an internal chitinous or calcareous shell; 8–10 appendages around the mouth (8 arms and 2 tentacles when present) lined with suckers or hooks; one pair of gills; highly developed eyes; a fused, tubelike funnel; an ink sac (lost in some species); chromatophores; and fins on the body (lost in some octopuses).

The living coleoids are the order Sepioidea (cuttlefishes, like Sepia; bobtail squids, Spirula); the order Teuthoidea (squids—nearshore myopsids, like Loligo; open-ocean oegopsids, like Ommastrephes); the order Vampyromorpha (the black, deep-sea vampire squid); and the order Octopoda (octopuses, argonauts, deep-sea finned or cirrate octopods). Living coleoids generally are fast, mobile predators with an advanced brain and central nervous system. See also Belemnoidea; Cephalopoda; Mollusca; Nautiloidea; Sepioidea; Vampyromorpha.

Coleoids Fossil range: Devonian or Carboniferous - Recent
Juvenile cephalopod from plankton Antarctica
Scientific classification
Kingdom: Animalia Phylum: Mollusca Class: Cephalopoda Subclass: Coleoidea Bather, 1888
Orders
†Belemnoidea †Aulacocerida †Belemnitida †Hematitida †Phragmoteuthida Neocoleoidea (most living cephalopods) ?†Boletzkyida Sepiida Sepiolida Spirulida Teuthida Octopoda Vampyromorphida

Subclass Coleoidea is the grouping of cephalopods containing all the primarily soft-bodied creatures. Unlike its sister group the Nautiloidea, which has a rigid outer shell for protection, the coleoids have at most an internal bone or shell that is used for buoyancy or support. Some species have lost their bone altogether, while in some it has been replaced by a cartilaginous support structure.

The major dividings of Coleoidea are based upon the number of arms or tentacles and their structure. The extinct and most primitive form, the Belemnoidea, presumably had ten equally sized arms, in five pairs numbered ventral to dorsal as I, II, III, IV and V. More modern species either modified or lost a pair of arms. The superorder Decapodiformes has arm pair IV modified into long tentacles with suckers generally only on the club-shaped distal end. Superorder Octopodiformes has modifications to arm pair II; it is significantly reduced and used only as a sensory filament in the Vampyromorphida, while Octopoda species have totally lost that arm pair.

Classification

• CLASS CEPHALOPODA
  • Subclass Nautiloidea: nautilus
  • Subclass †Ammonoidea: ammonites
  • Subclass Coleoidea
    • Division †Belemnoidea: extinct belemnoids
      • Genus †Jeletzkya
      • Order †Aulacocerida
      • Order †Hematitida
      • Order †Phragmoteuthida
      • Order †Belemnitida
    • Division Neocoleoidea
      • Superorder Decapodiformes
        • ?Order †Boletzkyida
        • Order Spirulida: Ram's Horn Squid
        • Order Sepiida: cuttlefish
        • Order Sepiolida: bobtail squid
        • Order Teuthida: squid
      • Superorder Octopodiformes
        • Order Vampyromorphida: Vampire Squid
        • Order Octopoda: octopus

References

• Bather, F.A. (1888). "Shell-growth in Cephalopoda (Siphonopoda)". Annals and Magazine of Natural History 6 (1): 298-310. 

External links

• CephBase: Coleoidea
• Tree of Life web project: Coleoidea

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