Eumetazoa (), also known as Epitheliozoa or Histozoa, is a proposed basal animal subkingdom as a sister group of Porifera (sponges).
Some phylogenetics once speculated the sponges and eumetazoans Evolution separately from different single-celled organisms, which would have meant that the animal kingdom does not form a clade (a complete grouping of all organisms descended from a common ancestor). However, genetic studies and some morphological characteristics, like the common presence of , now unanimously support a common origin.
Traditionally, eumetazoans are a major group of in the Five Kingdoms classification of Lynn Margulis and K. V. Schwartz, comprising the Radiata and Bilateria – all animals except the sea sponge.[ "Systema Naturae 2000 Taxon: Subkingdom Eumetazoa". . Retrieved February 2, 2006]
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
Bilateria 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 being-
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
Proarticulata are considered as stem
Bilateria by most authors
[Ivantsov, A. Yu. (2021). "Proarticulates—an extinct phylum of soft-bodied metazoans, or a group of vendobionts par excellence?" Symmetry. 13(2): 160. Full text. doi:10.3390/sym13020160.]. 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.
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