Deuterostomes are a major subgroup of animals, characterized by a particular pattern of embryonic development. In deuterostome development, the first opening that forms becomes the anus, while the mouth develops later. This is in contrast to protostomes, where the first opening becomes the mouth. Deuterostomes include vertebrates (like mammals, birds, reptiles, amphibians, and fish) as well as some invertebrates such as echinoderms (like starfish and sea urchins) and hemichordates.
