Other studies have presented evidence supporting Porifera as the sister to Parahoxozoa and Ctenophora as the sister group to the rest of animals (e.g. [5][6][7]), finding that nervous systems either evolved independently in ctenophores and parahoxozoans,[8] or were secondarily lost in poriferans.

[10] The cladogram, which is congruent with the vast majority of these phylogenomic studies, conveys this uncertainty with a polytomy.

[11] Parahoxozoa was defined by the presence of several gene (sub)classes (HNF, CUT, PROS, ZF, CERS, K50, S50-PRD), as well as Hox/ParaHox-ANTP from which the name of this clade originated.

Regardless of whether a ParaHox gene is ever definitively identified, Parahoxozoa, as originally defined, is monophyletic and therefore continues to be used as such.

[15] The original bilaterian is hypothesized to be a bottom dwelling worm with a single body opening.