Παρα-, para, "next to", and ζωα, zoa, "animals") are a taxon with sub-kingdom category that is located at the base of the phylogenetic tree of the animal kingdom in opposition to the sub-kingdom Eumetazoa; they group together the most primitive forms, characterized by not having proper tissues or that, in any case, these tissues are only partially differentiated.

On occasion, Parazoa reunites Porifera with Archaeocyatha, a group of extinct sponges sometimes considered a separate phylum.

They have been considered separate phyla,[1] however, the consensus is growing that Archaeocyatha was in fact a type of sponge that can be classified into Porifera.

[2] Some authors include in Parazoa the poriferous or sponge phyla and Placozoa on the basis of shared primitive characteristics: Both are simple, show a lack of true tissues and organs, have both asexual and sexual reproduction, and are invariably aquatic.

[citation needed] Some authors include the Placozoa,[4] a phylum long thought to consist of a single species, Trichoplax adhaerens, in the division, but sometimes it is also placed in the Agnotozoa subkingdom.