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From Wikipedia, the free encyclopedia

Eumetazoa (Greek: εὖ [eu], well + μετά [metá], after + ζῷον [zóon], animal) or Diploblasts, or Epitheliozoa, or Histozoa are a proposed basal animal clade as a sister group of the Porifera.[4][5][6][7][8]The basal Eumetazoan clades are the Ctenophora and the ParaHoxozoa. Placozoa is now also seen as an Eumetazoan in the Parahoxozoa.

Several other extinct or obscure life forms, such as Iotuba and Thectardis appear to have emerged in the group.[9] Characteristics of eumetazoans include true tissues organized into germ layers, the presence of neurons, and an embryo that goes through a gastrula stage.

Some phylogenists have speculated the sponges and eumetazoans evolved separately from single-celled organisms, which would mean 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, support a common origin.[10]

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.[11] 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.

It is divided into Grades Radiata and Bilateria.[citation needed]

Grade Radiata includes only Phylum Cnidaria.[citation needed]

Grade Bilateria includes bilateral symmetry that is the body of these animals can be cut into two identical halves in one plane that is they have left and right side of the body.

All the phyla from Platyhelminthes to Chordates are included in Grade Bilateria.

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Transcription

Contents

Taxonomy

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 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.

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.[12] 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.[13] 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.[14]

References

  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. Quartely 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. ^ Feuda, Roberto; Dohrmann, Martin; Pett, Walker; Philippe, Hervé; Rota-Stabelli, Omar; Lartillot, Nicolas; Wörheide, Gert; Pisani, Davide. "Improved Modeling of Compositional Heterogeneity Supports Sponges as Sister to All Other Animals". Current Biology. doi:10.1016/j.cub.2017.11.008.
  5. ^ 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.
  6. ^ 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". Current Biology. 27 (7): 958–967. doi:10.1016/j.cub.2017.02.031.
  7. ^ 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.
  8. ^ Laumer, Christopher E.; Gruber-Vodicka, Harald; Hadfield, Michael G.; Pearse, Vicki B.; Riesgo, Ana; Marioni, John C.; Giribet, Gonzalo (2017-10-11). "Placozoans are eumetazoans related to Cnidaria". bioRxiv: 200972. doi:10.1101/200972.
  9. ^ Martindale, Mark Q.; Kourakis, Matthew J. "Hox clusters:  Size doesn't matter". Nature. 399 (6738): 730–731. Bibcode:1999Natur.399..730M. doi:10.1038/21530.
  10. ^ Philippe, H.; Derelle, R.; Lopez, P.; et al. (April 2009). "Phylogenomics revives traditional views on deep animal relationships". Curr. Biol. 19 (8): 706–12. doi:10.1016/j.cub.2009.02.052. PMID 19345102.
  11. ^ Systema Naturae 2000 Taxon: Subkingdom Eumetazoa — retrieved February 2, 2006
  12. ^ 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.
  13. ^ 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.
  14. ^ 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.

External links

This page was last edited on 14 August 2018, at 10:14
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