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Eumetazoa

Eumetazoa, also known as Epitheliozoa or Histozoa, is a proposed basal animal subkingdom as a sister group of Porifera (sponges). The basal eumetazoan clades are the Ctenophora and the ParaHoxozoa. Placozoa is now also seen as a eumetazoan in the ParaHoxozoa. The competing hypothesis is the Myriazoa clade which states Ctenophora diverged earlier then Porifera, and Porifera instead makes a clade with Parahoxozoa, implying either sponges lost complexity or ctenophores developed their characteristics independently, maybe even a mix of both process. As far as April 2026 this questions remains unresolved and the dispute became somewhat personal and belic, with many scientists deciding to not participate into this debate. The subkingdom Parazoa is the other taxa, which includes primarily Porifera. Agnothozoa were once considered intermediary clade between Parazoa and Eumetazoa but now is largely considered a poliphyletic group of simplified eumetazoans. Though some archaic fossil groups may with weak evidence still be considered members of an intermediate clade. Parazoa is the main sister group to eumetazoans, forming clade Blastozoa/Diploblastozoa. Alternatively, Parazoa was considered as a sister group to Agnotozoa . Several other extinct or obscure life forms, such as Iotuba and Thectardis, may have emerged in the group. Characteristics of eumetazoans include true tissues organized into germ layers, the presence of neurons and muscles, and an embryo that goes through a gastrula stage.

Evolutionary origins
It has been suggested that one type of molecular clock and one approach to interpretation of the fossil record both place the evolutionary origins of eumetazoa in the Ediacaran. However, the earliest eumetazoans may not have left a clear impact on the fossil record and other interpretations of molecular clocks suggest the possibility of an earlier origin. The discoverers of Vernanimalcula describe it as the fossil of a bilateral triploblastic animal that appeared at the end of the Marinoan glaciation prior to the Ediacaran period, implying an even earlier origin for eumetazoans. Various ediacaran organisms have been tentatively classified as eumetazoans. But so far, very few Ediacaran organisms have been identified as definite eumetazoans like- Kimberella, Haootia and Dickinsonia. Ediacaran fossils preserve very little details so identifying one as an animal with true tissue is very difficult. Many extinct phyla have been proposed by many researchers that may fall under the clade. These are Proarticulata, Trilobozoa and Petalonamae. The inclusion of these within eumetazoa as well as the position of these within the clade is highly debated and sometimes considered speculative. The proarticulates are considered as stem bilaterians by most authors. Together the three phyla are grouped as the grade Vendobionta.The petalonamids are often considered as early diverging animals before animals with true tissue organisation started to appear. ==References== ==External links==
Source: Wikipedia ↗
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