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Chordata is a phylum of animals, named after their possession of a notochord at some point during their lives (embryonic, juvenile, or adult). Chordates have four other unifying characteristics, also possessed at some life stage: a dorsal nerve cord, an endostyle, a post-anal tail, and pharyngeal pouches. Most chordates have a spinal cord, and are therefore vertebrates.

The phylum includes several classes, the most well-known of which are vertebrates:

There are also several obscure non-vertebrate animals including the acorn worm, lancelet and hagfish.

Other common features include a single brain and a zig-zag muscle structure in the torso, although these are not unique to the chordates.

Scientists believe that the chordata are closest to the arthropoda (shelled, joint-legged animals such as insects and crustaceans), echinodermata (spiny-skinned animals such as starfish and sea urchins), and annelida (earthworms) in biology, due to common features such as segmentation, which are not seen in other phyla such as the mollusca (molluscs) or coelenterata (jellyfish and sea anemones).

See also