During the formation of the gastrula, a group of cells migrates towards the inside. The resultant sac forms the embryonic gut. The embryonic gut has an opening that opens to the outside and is called the blastopore. The blastopore may give rise to mouth or anus. In some organisms, blastopore develops into the anus. These organisms are called deuterostomes. The other organisms in which blastopore develops into the mouth are called protosomes. Echinoderms, hemichordates, and chordates are deuterostomes.
