ParaHoxozoa

ParaHoxozoa is a proposed group within taxonomy.  It would be a clade, above phylum but below a kingdom.  

It would include the Bilateria, the Placozoa and the Cnidarians.

 Characteristics 
Parahoxozoa is named after the groups of genes that scientists found in the organisms in it: (sub)classes (HNF, CUT, PROS, ZF, CERS, K50, S50-PRD) and Hox/ParaHox-ANTP. Some scientists said they thought a similar gene, ANTP, the NK gene, and the Cdx Parahox gene were also in sponges in the phylum Porifera, but for now, Parahoxozoa does not have sponges in it.

Scientists are not sure where to put Placozoa.  They think it could be a sister clade to the other Parahoxozoa (the Planulozoa hypothesis) or sister of Cnidaria.

 Planula-acoel, triploblasty, and bilaterian similarities 
The first bilateral organisms (the first living things that were symmetrical from side to side) were worms which lived on the bottom of bodies of water. This type of worm probably had only one opening in its body instead of both a mouth and an anus, as bilateral organisms do today. A through-gut may already have developed with the ctenophora. The through-gut, the tubelike digestive system with two ends, may have evolved when the organism's one hole closed in the middle. For example, Acoela look like the planula larvae of some cnidarians.

 References 

Category:Groups of phyla
Category:Animals