ParaHoxozoa

The Parahoxozoa are a proposed grouping of animals based on presence of at least a single Hox/ParaHox gene, uniting Placozoa, Cnidaria (jellyfish) and Bilateria, as well as Porifera (sponges). As originally proposed, this grouping excluded both Porifera and Ctenophora (comb jellies), however a ParaHox gene has since been found in some sponges, leaving ctenophores as the only non-Parahoxozoan animal phylum. The phylogenetic position of Ctenophora remains controversial, so it is not clear whether Parahoxozoa represents a monophyletic clade (as would be the case if Ctenophora is the sister group to all other animals) or if it is paraphyletic (if sponges are the sister group to all other animals). Nevertheless, some authors speculate "that a burst of evolutionary innovation in the genes responsible for electrical communication among nerve cells in our brains occurred over 600 million years ago in a common ancestor of" parahoxozoans.