Deuterostomes is a group that includes echinoderms, hemichordates, and chordates. Although these animals exhibit a wide variety of body plans, they share a mouth secondarily formed during embryo development, which it is believed to be an evolutionarily derived character present between a common ancestor and all its descendants (i.e., a synapomorphy). This oral cavity is formed by the invagination of the ectoderm layer opposite to the blastopore of the gastrula.
