Chordates

Chordates Temporal range: Terreneuvian – Holocene, 542–0 Ma PreЄ Є O S D C P T J K Pg N
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
Yunnanozoon ? Cephalochordata †Pikaiidae Olfactores †Haikouella Tunicata Craniata †Myllokunmingiidae †Palaeospondylus †Zhongxiniscus †Vetulicolia And see text

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A chordate is an animal belonging to the phylum Chordata; they possess a , a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail, for at least some period of their life cycle. Chordates are deuterostomes, as during the embryo development stage the anus forms before the mouth. They are also bilaterally symmetric coelomates. In the case of vertebrate chordates, the notochord is usually replaced by a vertebral column during development, and they may have body plans organized via segmentation.

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. There are also additional extinct taxa. The Vertebrata are sometimes considered as a subgroup of the clade Craniata, consisting of chordates with a skull; the Craniata and Tunicata compose the clade Olfactores.

Of the more than 65,000 living species of chordates, about half are bony fish of the class Osteichthyes. The world's largest and fastest animals, the blue whale and peregrine falcon respectively, are chordates, as are humans. Fossil chordates are known from at least as early as the Cambrian explosion.