Uberon Homology note : Presently, Cephalochordata, Urochordata, and Vertebrata are placed as subphyla of
the phylum Chordata, in which the overall organization of embryonic tissues (dorsal
hollow nerve cord, ventral digestive tract, axial notochord, and bilateral paraxial
mesoderm) is largely conserved. In contrast, the echinoderms and hemichordates are
sister groups of the chordates and they lack the notochord and paraxial mesoderm.
Thus, the basic mesodermal organization of vertebrates must have appeared first in
the common ancestor of the chordates.[well established][VHOG];