Chordates include all the vertebrates and some invertebrate allies that possess, for part or all of their lives, a structure called a notochord. The notochord is a stiff rod that helps support the body and runs parallel to the main nerve cord. In the vertebrates, these have evolved into the spinal column, which is reinforced and protected by cartilage or bone. The allied invertebrates in the chordates phylum include members that only have the notochord for part of their life: the sea squirts, lancelets and hagfish.

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