Deuterostomes (taxonomic term: Deuterostomia; from the Greek: "second mouth") are a superphylum of animals. They are a subtaxon of the Bilateria branch of the subregnum Eumetazoa, and are opposed to the protostomes. Deuterostomes are distinguished by their embryonic development; in deuterostomes, the first opening (the blastopore) becomes the anus, while in protostomes it becomes the mouth.

There are four living phyla of deuterostomes:

Phylum Chordata (vertebrates and their kin)
Phylum Echinodermata (starfishes, sea urchins, sea cucumbers, etc.)
Phylum Hemichordata (acorn worms and possibly graptolites)
Phylum Xenoturbellida (2 species of worm-like animals)