Vertebrates
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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