The ParaHoxozoa are a proposed basal Diploblast/Eumetazoa clade as sister of the Ctenophora. It consists of the Triploblasts/Bilateria as well as the Placozoa and Cnidaria.[1][2][3][4][5][6][7]

Temporal range: 605.2–0 Ma Ediacaran-Present
Scientific classification e
Kingdom: Animalia
Subkingdom: Eumetazoa
Clade: ParaHoxozoa
Ryan et al., 2010


The Parahoxozoa group was defined based on 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. It was later proposed[8][9] and contested[10] that a gene of the same class (ANTP) as the Hox/ParaHox, the NK gene and the Cdx Parahox gene, is also present in Porifera. Nevertheless, the Parahoxozoa as originally defined without Porifera may be a monophyletic clade, and continues to be used as such.[4]

















(610 mya)
(650 mya)
(680 mya)
(760 mya)
(950 mya)

The position of Placozoa is not clear, as it may be sister the remaining Parahoxozoa (the Planulozoa hypothesis) or sister to the Cnidaria.

Planula-acoel, triploblasty, and bilaterian similaritiesEdit

The original bilateria are hypothesized to be a bottom dwelling worm with a single body opening.[11] A through-gut may already have developed with the ctenophora however.[12] The through-gut may have developed from the corners of a single opening with lips fusing. E.g. Acoela resemble the planula larvae of some cnidaria, which exhibit some bilaterian symmetry. They are vermiformes, just as the cnidarian Buddenbrockia is.[13][14][15] Placozoa has been noted to resemble planula.[16] Usually, "Planulozoa" is to the exclusion of Placozoa, but not necessarily. In this case it appears synonymous with ParaHoxozoa.[17] Triploblasty developed before the Cnidara-Bilateria radiation as well.[18]


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