Deuterostomia is a subtaxon of the Bilateria branch of the subkingdom Eumetazoa, within Animalia, and are distinguished from protostomes by their deuterostomic embryonic development; in deuterostomes, the first opening ( the blastopore ) becomes the anus, while in protostomes, it becomes the mouth . ( There are some occurrences of deuterostomy among Protostomes .)
32.
In animals at least as complex as an earthworm, the embryo forms a dent on one side, the blastopore, which deepens to become the archenteron, the first phase in the formation of the proto " meaning " first " ) while the anus formed later as an opening made by the other end of the gut.
33.
In " Xenopus laevis " " Xbra " ( the " Xenopus " " T " homologue, also recently renamed " t " ) is expressed in the mesodermal marginal zone of the pre-gastrula embryo followed by localisation to the blastopore and notochord at the mid-gastrula stage.
