Deuterostomia is a major group in the animal kingdom that includes organisms whose embryonic development features a specific pattern. In these animals, the first opening that forms during development becomes the anus, while the mouth develops later. This contrasts with Protostomia, where the mouth forms first. The group encompasses several important phyla, including Chordata, which contains vertebrates like mammals and birds, and Echinodermata, which includes sea stars and sea urchins. Deuterostomes are characterized by their complex body structures and developmental processes, making them a key focus in evolutionary biology.