An animal in which the opening (blastopore) of the embryonic cavity (see archenteron) becomes the anus and the mouth forms as a secondary orifice. The name derives from Greek, meaning literally ‘second mouth’. Deuterostomes typically display radial cleavage of the blastula, indeterminate development (the fate of cells is not established until later stages of development), and enterocoelic formation of the coelom (i.e. by outpocketing of the embryonic gut). This contrasts with protostome development, in which the mouth forms from the blastopore. Most, but not all, animals exhibiting deuterostome development are members of the clade Deuterostomia, which includes the three phyla Hemichordata, Echinodermata, and Chordata.