The last common ancestor of all bilaterians is thought to have had four hox genes. most extant cnidarians have two hox genes, though some have three hox genes. on the basis of these observations, some have proposed that the ancestral cnidarian's were originally bilateral and, in stages, lost hox genes from their genomes. if true, this would mean that

If true this would  mean that the radial symmetry of extent cnidarians is secondarily derived rather than being an ancestral trait and also that the Cnidaria may someday replace Acoela as the basal bilaterians. Bilaterians, the first of which likely evolved in the Precambrian, are a step up in multicellular complexity from Radiata. Whereas Radiata develop from two embryonic tissue layers, the bilateria have a third tissue layer, the mesoderm, between the endoderm and ectoderm.