# Parazoa

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Ancestral subkingdom of animals

Parazoa Temporal range: Tonian–Present Pha. Proterozoic Archean Had. Sponge Scientific classification (obsolete as paraphyletic) Kingdom: Animalia Subkingdom: Parazoa Grant & Todd, 1838 Subgroups Porifera sensu lato (Eumetazoa hypothesis) Porifera sensu stricto (modern sponges, Eumetazoa hypothesis) Silicarea Demospongiae Hexactinellida Calcarea s.l. †Heteractinida Calcarea Homoscleromorpha Stromatoporoidea Sponges with cyath body plan †Cribricyatha? †Archeocyatha †Radiocyatha †Proarchaeocyathus †Eocyathispongia †Olgunidae †Otavia Ctenophora? (Myriazoa hypothesis) †"Vendobionta"? List of ediacaran genera for more. Synonyms Enantiozoa, Delage 1892 Porifera s.l.

**Parazoa** (**Parazoa**, gr. Παρα-, para, "next to", and ζωα, zoa, "animals") is an obsolete [subkingdom](/source/Kingdom_(biology)) that is located at the base of the phylogenetic tree of the [animal](/source/Animal) [kingdom](/source/Kingdom_(biology)) in opposition to the subkingdom [Eumetazoa](/source/Eumetazoa); they group together the most primitive forms, characterized by not having proper tissues or where, in any case, these tissues are only partially differentiated. It generally includes a single phylum, [Porifera](/source/Porifera), which lack [muscles](/source/Muscles), [nerves](/source/Nerves) and internal [organs](/source/Organ_(biology)), which in many cases resembles a cell colony rather than a multicellular organism itself. All other animals are eumetazoans), which do have differentiated tissues.

## Porifera and Archaeocyatha

[Porifera](/source/Porifera) and the long gone extinct [Archaeocyatha](/source/Archaeocyatha) show similarities such as benthic and sessile habitat and the presence of pores, with differences such as the presence of internal walls and septa in Archaeocyatha. 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] Many other fossil groups have uncertain affinity with porifera.[3]

## Porifera and Placozoa

Some authors include in Parazoa the poriferous or [sponge](/source/Sponge) [phyla](/source/Phylum) and [Placozoa](/source/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](/source/Reproduction), and are invariably aquatic. As animals, they are a group that in various studies are at the base of the phylogenetic tree, albeit in a [paraphyletic](/source/Paraphyletic) form. Of this group only surviving sponges, which belong to the phylum [Porifera](/source/Porifera), and *[Trichoplax](/source/Trichoplax)* in the phylum [Placozoa](/source/Placozoa).

Parazoa do not show any body symmetry (they are asymmetric); all other groups of animals show some kind of symmetry. There are currently 5000 species, 150 of which are freshwater. The larvae are planktonic and the adults are sessile. The Parazoa–Eumetazoa division has been estimated to be 940 million years ago.[4]

The Parazoa group is now considered paraphyletic.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] When referenced, it is sometimes considered an equivalent to the Porifera.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

Some authors include the [Placozoa](/source/Placozoa),[5] a phylum long thought to consist of a single species, *[Trichoplax adhaerens](/source/Trichoplax_adhaerens)*, in the division, but sometimes it is also placed in the Agnotozoa subkingdom.

## Phylogeny

According to the most up-to-date phylogeny, Porifera should not have a direct relationship with Placozoa. In any case, placozoans are likely simplified "coelenterates" without common characteristics with sponges.[6][7][8]

Animalia Porifera Eumetazoa Ctenophora ParaHoxozoa Placozoa Cnidaria Bilateria

## References

[Wikispecies](/source/Wikispecies) has information related to ***[Parazoa](https://species.wikimedia.org/wiki/Parazoa)***.

Wikimedia Commons has media related to [Parazoa](https://commons.wikimedia.org/wiki/Category:Parazoa).

1. **[^](#cite_ref-1)** Whittaker, R. H. (1969). New concepts of kingdoms or organisms. Science 163 (3863): 150–160.

1. **[^](#cite_ref-2)** Stephen M. Rowland 2001, [Archaeocyaths: A History of Phylogenetic Interpretation](https://www.jstor.org/stable/1307076?seq=1#page_scan_tab_contents) Journal of Paleontology Vol. 75, No. 6, 75th Anniversary Issue (Nov., 2001), pp. 1065-1078

1. **[^](#cite_ref-3)** Antcliffe, Jonathan B.; Callow, Richard H. T.; Brasier, Martin D. (2011). ["Giving the early fossil record of sponges a squeeze"](https://onlinelibrary.wiley.com/doi/10.1111/brv.12090). *Biological Reviews*. **89** (4): 972–1004. [doi](/source/Doi_(identifier)):[10.1111/brv.12090](https://doi.org/10.1111%2Fbrv.12090). [ISSN](/source/ISSN_(identifier)) [1464-7931](https://search.worldcat.org/issn/1464-7931). [PMID](/source/PMID_(identifier)) [24779547](https://pubmed.ncbi.nlm.nih.gov/24779547).

1. **[^](#cite_ref-4)** Nikoh, Naruo; Iwabe, Naoyuki; Kuma, Kei-ichi; Ohno, Mutsuhito; Sugiyama, Tsutomu; Watanabe, Yoko; Yasui, Kinya; Shi-cui, Zhang; Hori, Katsuji; Shimura, Yoshiro; Miyata, Takashi (July 1997). "An Estimate of Divergence Time of Parazoa and Eumetazoa and That of Cephalochordata and Vertebrata by Aldolase and Triose Phosphate Isomerase Clocks". *Journal of Molecular Evolution*. **45** (1): 97–106. [doi](/source/Doi_(identifier)):[10.1007/PL00006208](https://doi.org/10.1007%2FPL00006208). [PMID](/source/PMID_(identifier)) [9211740](https://pubmed.ncbi.nlm.nih.gov/9211740). [S2CID](/source/S2CID_(identifier)) [23710913](https://api.semanticscholar.org/CorpusID:23710913).

1. **[^](#cite_ref-5)** "Reviews glossary". Retrieved 2009-03-20.

1. **[^](#cite_ref-6)** Laumer, Christopher E.; Fernández, Rosa; Lemer, Sarah; Combosch, David; Kocot, Kevin M.; Riesgo, Ana; Andrade, Sónia C. S.; Sterrer, Wolfgang; Sørensen, Martin V.; Giribet, Gonzalo (10 July 2019). ["Revisiting metazoan phylogeny with genomic sampling of all phyla"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6650721). *Proceedings of the Royal Society B: Biological Sciences*. **286** (1906) 20190831. [doi](/source/Doi_(identifier)):[10.1098/rspb.2019.0831](https://doi.org/10.1098%2Frspb.2019.0831). [ISSN](/source/ISSN_(identifier)) [0962-8452](https://search.worldcat.org/issn/0962-8452). [PMC](/source/PMC_(identifier)) [6650721](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6650721). [PMID](/source/PMID_(identifier)) [31288696](https://pubmed.ncbi.nlm.nih.gov/31288696).

1. **[^](#cite_ref-7)** Laumer, Christopher E.; Gruber-Vodicka, Harald; Hadfield, Michael G.; Pearse, Vicki B.; Riesgo, Ana; Marioni, John C.; Giribet, Gonzalo (2018). ["Support for a clade of Placozoa and Cnidaria in genes with minimal compositional bias"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6277202). *eLife*. 2018, 7 e36278. [doi](/source/Doi_(identifier)):[10.7554/eLife.36278](https://doi.org/10.7554%2FeLife.36278). [PMC](/source/PMC_(identifier)) [6277202](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6277202). [PMID](/source/PMID_(identifier)) [30373720](https://pubmed.ncbi.nlm.nih.gov/30373720).

1. **[^](#cite_ref-8)** Roberto Feuda et al. 2017, [Improved Modeling of Compositional Heterogeneity Supports Sponges as Sister to All Other Animals](http://www.cell.com/current-biology/fulltext/S0960-9822(17)31453-7) Current Biology, Volume 27, Issue 24, p3864–3870.e4

v t e Extant animal phyla Domain Archaea Bacteria Eukaryota (major groups Metamonada Discoba Diaphoretickes Hacrobia Cryptista Rhizaria Alveolata Stramenopiles Plants Amorphea Amoebozoa Opisthokonta Animalia Fungi Mesomycetozoea) Animalia Porifera (sponges) Ctenophora (comb jellies) ParaHoxozoa (Planulozoa) Placozoa (Trichoplax and relatives) Cnidaria (jellyfish and relatives) Bilateria (Triploblasts) (see below↓) The phylogeny of the animal root is disputed; see also Eumetazoa Benthozoa Bilateria Bilateria Xenacoelomorpha (acoels and relatives) Chordata (vertebrates and relatives) Ambulacraria Echinodermata (starfish and relatives) Hemichordata (acorn worms and relatives) Protostomia Ecdysozoa Scalidophora Kinorhyncha (mud dragons) Priapulida (penis worms) Loricifera (corset animals) Cryptovermes Nematoida Nematoda (roundworms) Nematomorpha (horsehair worms) Panarthropoda Onychophora (velvet worms) Arthropoda (insects and relatives) Tardigrada (waterbears) Spiralia Gnathifera Chaetognatha (arrow worms) Gnathostomulida (jaw worms) M+R Micrognathozoa (Limnognathia) Rotifera (wheel animals inc. acanthocephalans) Platytrochozoa C+E Cycliophora (Symbion) Entoprocta or Kamptozoa Rouphozoa Platyhelminthes (flatworms) Gastrotricha (hairybacks) Mesozoa Orthonectida Dicyemida or Rhombozoa ?Monoblastozoa (Salinella) Lophotrochozoa Annelida (earth worms and relatives) Mollusca (snails and relatives) Nemertea (ribbon worms) Lophophorata Brachiopoda (lamp shells) B+P Bryozoa or Ectoprocta (moss animals) Phoronida (horseshoe worms) The phylogeny of Bilateria is disputed; see also Nephrozoa Deuterostomia Xenambulacraria Centroneuralia Major groups within phyla Sponges Demosponges Glass sponges Calcareous sponges Cnidarians Anthozoans inc. corals Medusozoans inc. jellyfish Myxozoans Chordates Lancelets Tunicates Vertebrates Echinoderms Sea lilies Asterozoans inc. starfish Echinozoans inc. sea urchins Hemichordates Acorn worms Pterobranchs Nematodes Chromadorea Enoplea Secernentea Arthropods Chelicerates inc. arachnids Myriapods Pancrustaceans inc. hexapods Rotifera Bdelloidea Monogononta Seisonidae Acanthocephala Platyhelminths Turbellaria Trematoda Monogenea Cestoda Ectoproctans Phylactolaemata Stenolaemata Gymnolaemata Annelids Polychaetes Clitellata Sipuncula Molluscs Gastropods Cephalopods Bivalves Chitons Tusk shells Phyla with ≥1000 extant species bolded Potentially dubious phyla †

Taxon identifiers Parazoa Wikidata: Q205716 Wikispecies: Parazoa Fauna Europaea: 54069 Fauna Europaea (new): f52ea61c-ee6d-4d35-860c-500c367dab3d Paleobiology Database: 82028

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Adapted from the Wikipedia article [Parazoa](https://en.wikipedia.org/wiki/Parazoa) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Parazoa?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.