The last common ancestor of all bilaterians is thought to have had four Hox genes (genes that regulate development of posterior-anterior axes and body segments). Most extant cnidarians have two Hox genes, except Nematostella, which has three Hox genes. On the basis of these observations, some have proposed that the ancestral cnidarians were originally bilateral and, in stages, lost Hox genes from their genomes. If true, this would mean that