Deuterostomes are a group of animals characterized by their embryonic development. In these organisms, the first opening that forms during the early stages of development becomes the anus, while the mouth develops later. This contrasts with protostomes, where the mouth forms first. Deuterostomes include a diverse range of species, such as chordates and echinoderms. The two main phyla of deuterostomes are Echinodermata, which includes starfish and sea urchins, and Chordata, which encompasses vertebrates like mammals, birds, and reptiles. This group is significant in the study of evolutionary biology due to its complex body structures and developmental processes.