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an inclusive term comprising animals of the three phyla Hemichordata, Echinodermata, and Chordata. The term “Deuterostomia” was introduced into the system of animal classification by the German zoologist K. Grobben in 1908. In contrast to the Protostomia, deuterostomes form a new mouth opening during their embryonic development that is independent of the protostoma, or blastopore (the latter usually becoming the anus). Deuterostomia have a secondary body cavity, or coelom, which develops from an out-pouching of the intestine. The endoskeleton is of mesodermal origin. The nervous system takes the form of an ectodermal plate with in-pouchings under the skin. The biochemistry of muscle contraction in Deuterostomia is characterized by the formation of creatine phosphate. The phyla Chaetognatha and Pogonophora are now also included among the Deuterostomia.
A. V. IVANOV