Eumetazoa

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Eumetazoans
Temporal range: Ediacaran - Present, 635–0 Ma
MolluscaScyphozoaChordataArthropodAnnelidaAnimalia diversity.jpg
About this image
Diversity of eumetazoans
Scientific classification e
Domain: Eukaryota
(unranked): Amorphea
(unranked): Obazoa
(unranked): Opisthokonta
(unranked): Holozoa
(unranked): Filozoa
Kingdom: Animalia
Subkingdom: Eumetazoa
Buetschli, 1910
Phyla
Synonyms

Eumetazoa (from Ancient Greek εὖ () 'well', μετά (metá) 'after', and ζῷον (zôion) 'animal'), also known as diploblasts, Epitheliozoa, or Histozoa, are a proposed basal animal clade as a sister group of the Porifera (sponges).[5][6][7][8][9] The basal eumetazoan clades are the Ctenophora and the ParaHoxozoa. Placozoa is now also seen as a eumetazoan in the ParaHoxozoa.

Several other extinct or obscure life forms, such as Iotuba and Thectardis, appear to have emerged in the group.[10] 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.

Some phylogenists once speculated the sponges and eumetazoans evolved 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 choanocytes, now unanimously support a common origin.[11]

Traditionally, eumetazoans are a major group of animals in the Five Kingdoms classification of Lynn Margulis and K. V. Schwartz, comprising the Radiata and Bilateria – all animals except the sponges.[12] When treated as a formal taxon Eumetazoa is typically ranked as a subkingdom. The name Metazoa has also been used to refer to this group, but more often refers to the Animalia as a whole. Many classification schemes do not include a subkingdom Eumetazoa.

Taxonomy[edit]

A widely accepted hypothesis, based on molecular data (mostly 18S rRNA sequences), divides Bilateria into four superphyla: Deuterostomia, Ecdysozoa, Lophotrochozoa, and Platyzoa (sometimes included in Lophotrochozoa). The last three groups are also collectively known as Protostomia.[citation needed]

However, some skeptics[who?] emphasize inconsistencies in the new data. The zoologist Claus Nielsen argues in his 2001 book Animal Evolution: Interrelationships of the Living Phyla for the traditional divisions of Protostomia and Deuterostomia.[citation needed]

Evolutionary origins[edit]

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.[13] 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.[14] 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.[15]

References[edit]

  1. ^ Lankester, Ray (1877). "Notes on the Embryology and classification of the Animal kingdom: comprising a revision of speculations relative to the origin and significance of the germ-layers". Quarterly Journal of Microscopical Science (N.S.), No. 68: 399–454.
  2. ^ Beklemishev, V. L. The basis of the comparative anatomy of the invertebrates [Основы сравнительной анатомии беспозвоночных]. 1st ed., 1944; 2nd ed., 1950; 3rd ed. (2 vols.), 1964. English translation, 1969, [1]. Akademia Nauk, Moscow, Leningrad.
  3. ^ Ax, Peter (2012-12-06). Multicellular Animals: A new Approach to the Phylogenetic Order in Nature. Springer Science & Business Media. ISBN 9783642801143.
  4. ^ Ulrich, W. (1950). "Begriff und Einteilung der Protozoen". In Grüneberg, H. (ed.). Moderne Biologie. Festschrift zum 60. Geburtstag von Hans Nachtsheim (in German). Berlin: Peters. pp. 241–250.
  5. ^ Feuda, Roberto; Dohrmann, Martin; Pett, Walker; Philippe, Hervé; Rota-Stabelli, Omar; Lartillot, Nicolas; Wörheide, Gert; Pisani, Davide (2017). "Improved Modeling of Compositional Heterogeneity Supports Sponges as Sister to All Other Animals". Current Biology. 27 (24): 3864–3870.e4. doi:10.1016/j.cub.2017.11.008. PMID 29199080.
  6. ^ Pisani, Davide; Pett, Walker; Dohrmann, Martin; Feuda, Roberto; Rota-Stabelli, Omar; Philippe, Hervé; Lartillot, Nicolas; Wörheide, Gert (15 December 2015). "Genomic data do not support comb jellies as the sister group to all other animals". Proceedings of the National Academy of Sciences. 112 (50): 15402–15407. Bibcode:2015PNAS..11215402P. doi:10.1073/pnas.1518127112. PMC 4687580. PMID 26621703.
  7. ^ Simion, Paul; Philippe, Hervé; Baurain, Denis; Jager, Muriel; Richter, Daniel J.; Franco, Arnaud Di; Roure, Béatrice; Satoh, Nori; Quéinnec, Éric (3 April 2017). "A Large and Consistent Phylogenomic Dataset Supports Sponges as the Sister Group to All Other Animals" (PDF). Current Biology. 27 (7): 958–967. doi:10.1016/j.cub.2017.02.031. PMID 28318975. S2CID 4560353.
  8. ^ Giribet, Gonzalo (1 October 2016). "Genomics and the animal tree of life: conflicts and future prospects". Zoologica Scripta. 45: 14–21. doi:10.1111/zsc.12215.
  9. ^ Laumer, Christopher E; Gruber-Vodicka, Harald; Hadfield, Michael G; Pearse, Vicki B; Riesgo, Ana; Marioni, John C; Giribet, Gonzalo (2018-10-30). "Support for a clade of Placozoa and Cnidaria in genes with minimal compositional bias". eLife. 7. doi:10.7554/elife.36278. ISSN 2050-084X. PMC 6277202. PMID 30373720.
  10. ^ Martindale, Mark Q.; Kourakis, Matthew J. (1999). "Hox clusters: Size doesn't matter". Nature. 399 (6738): 730–731. Bibcode:1999Natur.399..730M. doi:10.1038/21530. PMID 10391234. S2CID 43414178.
  11. ^ H., Philippe; Derelle, R.; Lopez, P.; et al. (April 2009). "Phylogenomics revives traditional views on deep animal relationships". Current Biology. 19 (8): 706–712. doi:10.1016/j.cub.2009.02.052. PMID 19345102. S2CID 15282843.
  12. ^ "Systema Naturae 2000 Taxon: Subkingdom Eumetazoa". Archived 2009-03-22 at the Wayback Machine. Retrieved February 2, 2006
  13. ^ Peterson KJ, Butterfield NJ (July 2005). "Origin of the Eumetazoa: testing ecological predictions of molecular clocks against the Proterozoic fossil record". Proc. Natl. Acad. Sci. U.S.A. 102 (27): 9547–52. Bibcode:2005PNAS..102.9547P. doi:10.1073/pnas.0503660102. PMC 1172262. PMID 15983372.
  14. ^ Blair, J. E.; Hedges, S. B. (March 2005). "Molecular clocks do not support the Cambrian explosion". Molecular Biology and Evolution. 22 (3): 387–390. doi:10.1093/molbev/msi039. PMID 15537810.
  15. ^ Chen, J.-Y.; Bottjer, D.J.; Oliveri, P.; Dornbos, S.Q.; Gao, F.; Ruffins, S.; Chi, H.; Li, C.-W.; Davidson, E.H.; et al. (9 July 2004). "Small bilaterian fossils from 40 to 55 million years before the Cambrian". Science. 305 (5681): 218–222. Bibcode:2004Sci...305..218C. doi:10.1126/science.1099213. PMID 15178752. S2CID 115443209.

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