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Chordate

Chordates
Temporal range:
TerreneuvianHolocene, 542–0 Ma
Pristella maxillaris.jpg
The X-ray tetra (Pristella maxillaris) is one of the few chordates with a visible backbone. The spinal cord is housed within its backbone.
Scientific classification
Kingdom: Animalia
Subkingdom: Eumetazoa
Clade: Bilateria
Clade: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Haeckel, 1874
Subgroups

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A chordate is any animal belonging to the phylum Chordata, possessing a , a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail for at least some period of its life cycle. The Chordata, together with sister clade Ambulacraria, form the deuterostomes as in the embryo development stage the anus forms before the mouth.

Taxonomically, the phylum includes the subphyla Vertebrata, which includes fish, amphibians, reptiles, birds, and mammals; Tunicata, which includes salps and sea squirts; and Cephalochordata, comprising the lancelets.

Members of the Chordata are bilaterally symmetric, deuterostome coelomates. Vertebrate chordates can have body plans organized via segmentation.

Hemichordata, which includes the acorn worms, has been presented as a fourth chordate subphylum, but it now is usually treated as a separate phylum. It, along with the Echinodermata, which includes starfish, sea urchins, sea cucumbers, and crinoids, are the chordates' closest taxon Ambulacraria. Fossil chordates are known from at least as early as the Cambrian explosion.



  • A notochord, a fairly stiff rod of cartilage that extends along the inside of the body. Among the vertebrate sub-group of chordates the notochord develops into the spine, and in wholly aquatic species this helps the animal to swim by flexing its tail.
  • A dorsal neural tube. In fish and other vertebrates, this develops into the spinal cord, the main communications trunk of the nervous system.
  • Pharyngeal slits. The pharynx is the part of the throat immediately behind the mouth. In fish, the slits are modified to form gills, but in some other chordates they are part of a filter-feeding system that extracts particles of food from the water in which the animals live.
  • Post-anal tail. A muscular tail that extends backwards behind the anus.
  • An endostyle. This is a groove in the ventral wall of the pharynx. In filter-feeding species it produces mucus to gather food particles, which helps in transporting food to the esophagus. It also stores iodine, and may be a precursor of the vertebrate thyroid gland.
  • Pigmentation : Chordata are not capable of blue pigmentation, that is to say blue skin pigmentation. Blue skin pigmentation is not to be confused with the biological alteration of (for example) feathers in birds—which appear blue via an evolved prism mechanism in the feather structure.
  • All Chordata are deuterostomes. This means that, during the embryo development stage, the anus forms before the mouth.
  • Class (lancelets)
  • Class †Placodermi (Paleozoic armoured forms; paraphyletic in relation to all other gnathostomes)
  • Class Chondrichthyes (cartilaginous fish; 900+ species)
  • Class †Acanthodii (Paleozoic "spiny sharks"; paraphyletic in relation to Chondrichthyes)
  • Superclass Osteichthyes (bony fish; 30,000+ species)
  • Superclass Tetrapoda (four-limbed vertebrates; 28,000+ species) (The classification below follows Benton 2004, and uses a synthesis of rank-based Linnaean taxonomy and also reflects evolutionary relationships. Benton included the Superclass Tetrapoda in the Subclass Sarcopterygii in order to reflect the direct descent of tetrapods from lobe-finned fish, despite the former being assigned a higher taxonomic rank.)
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