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Vertebrata, which is the largest part of Chordata. Primitive chordates don't have vertebrae.
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Vertebrata

Vertebrata is a group that contains various organisms which possess vertebrae (backbones). Animals that belong to the group are called vertebrates, and they include mammals, birds, fish, amphibians, and reptiles. The backbones in the animals extends from the head to the tail, and it encloses and protects the main nerve cord. The body of vertebrates is divided into trunk, and tail regions. They also possess a unique tube shaped brain, a distinct head, and three pairs of sense organs.