Parazoa

{{automatic taxobox

| fossil_range = {{long fossil range|760|0|Tonian –Present}}

| image = SpongeColorCorrect.jpg

| image_caption = Sponge

| taxon = Parazoa

| authority = Grant & Todd, 1838

| subdivision_ranks = Taxa

| subdivision =

Euparazoa/ Porifera s.l (Eumetazoa hypothesis)
Porifera s.s {{small|(Mordern sponges)}} (Eumetazoa/Complexa hypothesis; see below)
Cyatha {{small| (Sponges with cyath (Seemingly rusty) body plan)}} (Archaeocyatha s.lmo or sensu latissimo)
Eucyatha (Archaeocyatha s.l)
Radiozoa (Radiocyatha s.l)
Cribricyatha{{extinct}}
Radiocyatha{{extinct}}
Archaeocyatha{{extinct}}
Eocyathispongia{{extinct}} (Monotypic member of class protocyatha)
Otavia{{extinct}} (Sole member of Protospongia)
Ctenophora? (Myriazoa/Complexa hypothesis)
Vendobionta{{extinct}} (Always)
Placozoa?

See List of ediacaran genera for more (Select creatures only)

|synonyms = *Enantiozoa, Delage 1892

Porifera s.lmo

}}

Parazoa (Parazoa, gr. Παρα-, para, "next to", and ζωα, zoa, "animals") are a taxon with subkingdom category that is located at the base of the phylogenetic tree of the animal kingdom in opposition to the subkingdom 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. They generally group a single phylum, Porifera, which lack muscles, nerves and internal organs, which in many cases resembles a cell colony rather than a multicellular organism itself. All other animals are eumetazoans and Agnotozoans (Agnotozoans are possibly fake or even nonexistent in studies), which do have differentiated tissues.

On occasion, Parazoa reunites Porifera with Archaeocyatha, a group of extinct sponges sometimes considered a separate phylum. In other cases, Placozoa is included, depending on the authors.

Parazoa can be sister to “Complexa” With Parahoxozoa and agnotozoa together as complexa, being a sister group to Parazoa.

Porifera and Archaeocyatha

Porifera and 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,Whittaker, R. H. (1969). New concepts of kingdoms or organisms. Science 163 (3863): 150–160. however, the consensus is growing that Archaeocyatha was in fact a type of sponge that can be classified into Porifera.Stephen M. Rowland 2001, [https://www.jstor.org/stable/1307076?seq=1#page_scan_tab_contents Archaeocyaths: A History of Phylogenetic Interpretation] Journal of Paleontology Vol. 75, No. 6, 75th Anniversary Issue (Nov., 2001), pp. 1065-1078

Porifera and Placozoa

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. As animals, they are a group that in various studies are at the base of the phylogenetic tree, albeit in a paraphyletic form. Of this group only surviving sponges, which belong to the phylum Porifera, and Trichoplax in the phylum 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.{{cite journal|author1=Nikoh, Naruo |author2=Iwabe, Naoyuki |author3=Kuma, Kei-ichi |author4=Ohno, Mutsuhito |author5=Sugiyama, Tsutomu |author6=Watanabe, Yoko |author7=Yasui, Kinya |author8=Shi-cui, Zhang |author9=Hori, Katsuji |author10=Shimura, Yoshiro |author11=Miyata, Takashi |title=An Estimate of Divergence Time of Parazoa and Eumetazoa and That of Cephalochordata and Vertebrata by Aldolase and Triose Phosphate Isomerase Clocks|journal=Journal of Molecular Evolution |date=July 1997|volume=45|number=1|pages=97–106|doi=10.1007/PL00006208|pmid=9211740 |s2cid=23710913 }}

The Parazoa group is now considered paraphyletic.{{cn|date=August 2022}} When referenced, it is sometimes considered an equivalent to the Porifera.{{cn|date=August 2022}}

Some authors include the Placozoa,"Reviews glossary". Retrieved 2009-03-20. 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.

Phylogeny

According to the most up-to-date phylogeny, Porifera should not have a direct relationship with Placozoa. In any case, placozoans have simplified coelenterates without common characteristics with sponges.{{Cite journal|last1=Laumer|first1=Christopher E.|last2=Fernández|first2=Rosa|last3=Lemer|first3=Sarah|last4=Combosch|first4=David|last5=Kocot|first5=Kevin M.|last6=Riesgo|first6=Ana|last7=Andrade|first7=Sónia C. S.|last8=Sterrer|first8=Wolfgang|last9=Sørensen|first9=Martin V.|last10=Giribet|first10=Gonzalo|title=Revisiting metazoan phylogeny with genomic sampling of all phyla|journal=Proceedings of the Royal Society B: Biological Sciences|language=en|volume=286|issue=1906|pages=20190831|doi=10.1098/rspb.2019.0831|issn=0962-8452|pmc=6650721|date=10 July 2019|pmid=31288696}}{{Cite journal |last1=Laumer |first1=Christopher E. |last2=Gruber-Vodicka |first2=Harald |last3=Hadfield |first3=Michael G. |last4=Pearse |first4=Vicki B. |last5=Riesgo |first5=Ana |last6=Marioni |first6=John C. |last7=Giribet |first7=Gonzalo |year=2018 |title=Support for a clade of Placozoa and Cnidaria in genes with minimal compositional bias |journal=eLife |volume=2018;7 |pages=e36278 |doi=10.7554/eLife.36278 |pmid=30373720 |pmc=6277202 |doi-access=free }}Roberto Feuda et al. 2017, [http://www.cell.com/current-biology/fulltext/S0960-9822(17)31453-7 Improved Modeling of Compositional Heterogeneity Supports Sponges as Sister to All Other Animals] Current Biology, Volume 27, Issue 24, p3864–3870.e4

{{Clade | style=font-size:100%;line-height:100%

|label1=Animalia

| 1={{Clade

|1=Porifera

|label2=Eumetazoa

|2={{Clade

|1=Ctenophora

|label2=ParaHoxozoa

|2={{Clade

|1=Bilateria

|2={{Clade

|1=Cnidaria

|2=Placozoa}}}}}}}}}}

References

External links

Category:Parazoa

Category:Animals