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Urmetazoan

May 08, 2024

The Urmetazoan is the hypothetical last common ancestor of all animals, or metazoans. It is universally accepted to be a multicellular heterotroph — with the novelties of a germline and oogamy, an extracellular matrix (ECM) and basement membrane, cell-cell and cell-ECM adhesions and signaling pathways, collagen IV and fibrillar collagen, different cell types (as well as expanded gene and protein families), spatial regulation and a complex developmental plan, and relegated unicellular stages.[1]

Choanoflagellates edit

All animals are posited to have evolved from a flagellated eukaryote. Their closest known living relatives are the choanoflagellates, collared flagellates whose cell morphology is similar to the choanocyte cells of certain sponges.

Molecular studies place animals in a supergroup called the opisthokonts, which also includes the choanoflagellates, fungi, and a few small parasitic protists. The name comes from the posterior location of the flagellum in motile cells, such as most animal spermatozoa, whereas other eukaryotes tend to have anterior flagella as well.

Hypotheses edit

Several different hypotheses for the animals' last common ancestor have been suggested.

  • The placula hypothesis, proposed by Otto Bütschli, holds that the last common ancestor of animals was an amorphous blob with no symmetry or axis. The center of this blob rose slightly above the silt, forming a hollow that aided feeding on the sea floor underneath. As the cavity grew deeper and deeper, the organisms resembled a thimble, with an inside and an outside.[2] This body shape is found in sponges and cnidaria. This explanation leads to the formation of the bilaterian body plan; the urbilaterian would develop its symmetry when one end of the placula became adapted for forward movement, resulting in left-right symmetry.[2]
  • The planula hypothesis, proposed by Bütschli, suggests that metazoa are derived from planula; that is, the larva of certain cnidaria, or the adult form of the placozoans. Under this hypothesis, the larva became sexually mature through paedomorphosis, and could reproduce without passing through a sessile phase.
  • The gastraea hypothesis was proposed by Ernst Haeckel in 1874,[3] shortly after his work on the calcareous sponges. He proposed that this group of sponges is monophyletic with all eumetazoans, including the bilaterians. This suggests that the gastrulation and the gastrula stage are universal for eumetazoans. It has been perceived as problematic that gastrulation by invagination is by no means universal among eumetazoans. Only recently has an invagination been confirmed in a Calcarea sponge, albeit too early to form a remaining inner space (archenteron).[4]
  • The bilaterogastraea hypothesis was developed by Gösta Jägersten as an adaptation of Ernst Haeckel's Gastraea hypothesis. He proposed that the Bilaterogastraea have a two-stage life cycle, with a pelagic juvenile and a benthic adult stage. The invagination of the original gastrula stage he saw as bilaterally symmetric rather than radially symmetric.

See also edit

References edit

  1. ^ Ros-Rocher Núria, Pérez-Posada Alberto, Leger Michelle M. and Ruiz-Trillo Iñaki. 2021 The origin of animals: an ancestral reconstruction of the unicellular-to-multicellular transition Open Biol. 11:200359. 200359. http://doi.org/10.1098/rsob.200359
  2. ^ a b Schierwater, B.; Eitel, M.; Jakob, W.; Osigus, J.; Hadrys, H.; Dellaporta, L.; Kolokotronis, O.; Desalle, R. (January 2009). Penny, David (ed.). "Concatenated Analysis Sheds Light on Early Metazoan Evolution and Fuels a Modern "Urmetazoon" Hypothesis". PLOS Biology. 7 (1): e20. doi:10.1371/journal.pbio.1000020. ISSN 1544-9173. PMC 2631068. PMID 19175291.
  3. ^ Haeckel, E. 1874. Die Gastraea-Theorie, die phylogenetische Classification des Thierreichs und die Homologie der Keimblätter. Jenaische Zeitschr. Naturwiss. 8:1-55.
  4. ^ Sally P Leys; Dafne Eerkes-Medrano (1 April 2005). "Gastrulation in Calcareous Sponges: In Search of Haeckel's Gastraea" (PDF). Integrative and Comparative Biology. 45 (2): 342–351. doi:10.1093/ICB/45.2.342. ISSN 1540-7063. PMID 21676779. Wikidata Q54502332.

External links edit

  • (Taxonomicon)
  • (Systema Naturae 2000)
  • Vitae (BioLib)
  • Wikispecies – a free directory of life

May 08, 2024
urmetazoan, hypothetical, last, common, ancestor, animals, metazoans, universally, accepted, multicellular, heterotroph, with, novelties, germline, oogamy, extracellular, matrix, basement, membrane, cell, cell, cell, adhesions, signaling, pathways, collagen, f. The Urmetazoan is the hypothetical last common ancestor of all animals or metazoans It is universally accepted to be a multicellular heterotroph with the novelties of a germline and oogamy an extracellular matrix ECM and basement membrane cell cell and cell ECM adhesions and signaling pathways collagen IV and fibrillar collagen different cell types as well as expanded gene and protein families spatial regulation and a complex developmental plan and relegated unicellular stages 1 Contents 1 Choanoflagellates 2 Hypotheses 3 See also 4 References 5 External linksChoanoflagellates editAll animals are posited to have evolved from a flagellated eukaryote Their closest known living relatives are the choanoflagellates collared flagellates whose cell morphology is similar to the choanocyte cells of certain sponges Molecular studies place animals in a supergroup called the opisthokonts which also includes the choanoflagellates fungi and a few small parasitic protists The name comes from the posterior location of the flagellum in motile cells such as most animal spermatozoa whereas other eukaryotes tend to have anterior flagella as well Hypotheses editSeveral different hypotheses for the animals last common ancestor have been suggested The placula hypothesis proposed by Otto Butschli holds that the last common ancestor of animals was an amorphous blob with no symmetry or axis The center of this blob rose slightly above the silt forming a hollow that aided feeding on the sea floor underneath As the cavity grew deeper and deeper the organisms resembled a thimble with an inside and an outside 2 This body shape is found in sponges and cnidaria This explanation leads to the formation of the bilaterian body plan the urbilaterian would develop its symmetry when one end of the placula became adapted for forward movement resulting in left right symmetry 2 The planula hypothesis proposed by Butschli suggests that metazoa are derived from planula that is the larva of certain cnidaria or the adult form of the placozoans Under this hypothesis the larva became sexually mature through paedomorphosis and could reproduce without passing through a sessile phase The gastraea hypothesis was proposed by Ernst Haeckel in 1874 3 shortly after his work on the calcareous sponges He proposed that this group of sponges is monophyletic with all eumetazoans including the bilaterians This suggests that the gastrulation and the gastrula stage are universal for eumetazoans It has been perceived as problematic that gastrulation by invagination is by no means universal among eumetazoans Only recently has an invagination been confirmed in a Calcarea sponge albeit too early to form a remaining inner space archenteron 4 The bilaterogastraea hypothesis was developed by Gosta Jagersten as an adaptation of Ernst Haeckel s Gastraea hypothesis He proposed that the Bilaterogastraea have a two stage life cycle with a pelagic juvenile and a benthic adult stage The invagination of the original gastrula stage he saw as bilaterally symmetric rather than radially symmetric The phagocytella hypothesis was proposed by Elie Metchnikoff See also editEvolution of nervous systems Origin and subsequent variation and development of neurons and neural tissues and organs Ikaria wariootia Early bilaterian organism fossil species LUCA Most recent common ancestor of all current life on Earth Mitochondrial Eve Matrilineal most recent common ancestor of all living humans Organism Individual living being Outline of biology Outline of subdisciplines within biology Outline of life forms Overview of and topical guide to life forms Timeline of the evolutionary history of life Urbilaterian Possible simple urbilateran candidateReferences edit Ros Rocher Nuria Perez Posada Alberto Leger Michelle M and Ruiz Trillo Inaki 2021 The origin of animals an ancestral reconstruction of the unicellular to multicellular transition Open Biol 11 200359 200359 http doi org 10 1098 rsob 200359 a b Schierwater B Eitel M Jakob W Osigus J Hadrys H Dellaporta L Kolokotronis O Desalle R January 2009 Penny David ed Concatenated Analysis Sheds Light on Early Metazoan Evolution and Fuels a Modern Urmetazoon Hypothesis PLOS Biology 7 1 e20 doi 10 1371 journal pbio 1000020 ISSN 1544 9173 PMC 2631068 PMID 19175291 Haeckel E 1874 Die Gastraea Theorie die phylogenetische Classification des Thierreichs und die Homologie der Keimblatter Jenaische Zeitschr Naturwiss 8 1 55 Sally P Leys Dafne Eerkes Medrano 1 April 2005 Gastrulation in Calcareous Sponges In Search of Haeckel s Gastraea PDF Integrative and Comparative Biology 45 2 342 351 doi 10 1093 ICB 45 2 342 ISSN 1540 7063 PMID 21676779 Wikidata Q54502332 External links editBiota Taxonomicon Life Systema Naturae 2000 Vitae BioLib Wikispecies a free directory of life Portals nbsp Biology nbsp Evolutionary biology nbsp Marine life nbsp Paleontology Retrieved from https en wikipedia org w index php title Urmetazoan amp oldid 1211865683, wikipedia, wiki, 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