|The X-ray tetra (Pristella maxillaris) is ane o the few chordates wi a visible backbone. The spinal cord is hoosed within its backbone.|
Chordates, members o the phylum Chordata, are deuterostome ainimals possessin a notochord, a hollae dorsal nerve cord, pharyngeal slits, an endostyle, an a post-anal tail for at least some period o their life cycles. Taxonomically, the phylum includes the subphyla Vertebrata, includin mammals, fish, amphibians, reptiles, birds; Tunicata, includin salps an sea squirts; and Cephalochordata, comprisin the lancelets. For a recent concise review o chordate relationships, see Holland, N. D. 2005, Chordates. Curr. Biol. 15: R911-R914.
The phylum Hemichordata includin the acorn worms haes been presented as a fowert chordate subphylum, but it nou is uisually treatit as a separate phylum. It, alang wi the echinoderm phylum, includin starnfish, sea urchins, an sea cucumbers an thair kin, are the chordates' closest relatives. Primitive chordates are kent frae at least as early as the Cambrian explosion.
Thare are mair than 75,000 livin species o chordates, aboot hauf o which are bony fish o the class osteichthyes. The warld's lairgest ainimal, the blue whale, an fastest ainimal, the peregrine falcon, are chordates.