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'''Chordata''' is a [[phylum]] of [[animal]]s, named after their common feature - possession of a [[spinal cord]].

'''Chordata''' is a [[phylum]] of [[animal]]s, 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 [[class (biology)|classes]]:

The phylum includes several [[class (biology)|classes]], the most well-known of which are vertebrates:

*'''Mammalia''' - the [[mammal]]s

*'''Mammalia''' - the [[mammal]]s, such as the cats and the great apes

*'''Aves''' - the [[bird]]s

*'''Aves''' - the [[bird]]s

*'''Reptilia''' - The [[reptile]]s

*'''Reptilia''' - The [[reptile]]s, such as the (extinct) [[dinosaurs]]

*'''Amphibia''' - the [[amphibian]]s (such as [[frog]]s, [[newt]]s and [[salamander]]s)

*'''Amphibia''' - the [[amphibian]]s (such as [[frog]]s, [[newt]]s and [[salamander]]s)

*'''Pisces''' - the [[fish]]

*'''Pisces''' - the [[fish]]

There are also several obscure animals including the [[acorn worm]], [[lancelet]] and [[hagfish]].

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

Apart from the spinal cord, other common features include a single [[brain]] and a zig-zag [[muscle]] structure in the [[torso]].

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 [[insect]]s and [[crustacean]]s), [[echinodermata]] (spiny-skinned animals such as [[starfish]] and [[sea urchin]]s), and [[annelida]] (earthworms) in biology, due to common features such as [[segment]]ation, which are not seen in other phyla such as the [[mollusca]] (molluscs) or [[coelenterata]] ([[jellyfish]] and [[sea anemone]]s).

Scientists believe that the chordata are closest to the [[arthropoda]] (shelled, joint-legged animals such as [[insect]]s and [[crustacean]]s), [[echinodermata]] (spiny-skinned animals such as [[starfish]] and [[sea urchin]]s), and [[annelida]] (earthworms) in biology, due to common features such as [[segment]]ation, which are not seen in other phyla such as the [[mollusca]] (molluscs) or [[coelenterata]] ([[jellyfish]] and [[sea anemone]]s).