Deuterostome

Deuterostomes (from Ancient Greek δεύτερος (deúteros) 'second' and στόμα (stóma) 'mouth') are bilaterian animals of the superphylum Deuterostomia (/ˌdjuːtərəˈstoʊmi.ə/), which are typically characterized by their blastopore becoming their anus during embryonic development. Deuterostomia comprises three phyla: Chordata, Echinodermata, Hemichordata, and the extinct clade Cambroernida.

In deuterostomes, the developing embryo's first opening (the blastopore) becomes the anus and cloaca, while the mouth is formed at a different site later on. This was initially the group's distinguishing characteristic, but deuterostomy has since been discovered among protostomes as well. The deuterostomes are also known as enterocoelomates, because their coelom develops through pouching of the gut, enterocoely.

Deuterostomia's sister clade is Protostomia, animals that develop mouth first and whose digestive tract development is more varied. Protostomia includes the ecdysozoans and spiralians. Together with the Xenacoelomorpha, these constitute the large clade Bilateria, i.e. animals with bilateral symmetry and three germ layers.