Chordate

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
Cephalochordata †Pikaiidae Olfactores †Haikouella Tunicata Craniata †Myllokunmingiidae †Palaeospondylus † Zhongxiniscus And see text

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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.