The group of animals to which the belong is called the deuterostomes.
Deuterostome means “second mouth”, so called because the mouth develops from the second opening into the embryonic gut. The first opening (the blastopore) develops into the anus. The body cavity (coelom) develops from buds off the gut. Compare this with the other major group of animals, the .
As well as the vertebrates, this group includes starfish and sea urchins (Echinodermata), arrow worms (Chaetognatha) and lamp shells (Brachiopoda).
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