Protostome

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Protostomia (/ˌproʊtəˈstoʊmi.ə/) is the clade of animals once thought to be characterized by the creature's blastopore becoming its mouth during embryonic development. This nature has since been discovered to be extremely variable among Protostomia's members, although the reverse is typically true of its sister clade, Deuterostomia.[1][2] Well-known examples of protostomes are arthropods, molluscs, annelids, flatworms and nematodes. They are also called schizocoelomates since schizocoely typically occurs in them.

Together with the Deuterostomia and Xenacoelomorpha, these form the clade Bilateria, animals with bilateral symmetry, anteroposterior axis and three germ layers.[3]

Protostomy

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In animals at least as complex as earthworms, the first phase in gut development involves the embryo forming a dent on one side (the blastopore) which deepens to become its digestive tube (the archenteron). In the sister-clade, the deuterostomes (Template:Lit), the original dent becomes the anus while the gut eventually tunnels through to make another opening, which forms the mouth. The protostomes (from Greek Script error: No such module "Lang". Script error: No such module "lang". 'first' + Script error: No such module "Lang". Script error: No such module "lang". 'mouth') were so named because it was once believed that in all cases the embryological dent formed the mouth while the anus was formed later, at the opening made by the other end of the gut.[4][1] It is now known that the fate of the blastopore among protostomes is extremely variable; while the evolutionary distinction between deuterostomes and protostomes remains valid, the descriptive accuracy of the name protostome is disputable.[1]

Protostome and deuterostome embryos differ in several other ways. Secondary body cavities (coeloms) generally form by schizocoely, where the coelom forms out of a solid mass of embryonic tissue splitting away from the rest, instead of by enterocoelic pouching, where the coelom would otherwise form out of in-folded gut walls.[5]

Evolution

The common ancestor of protostomes and deuterostomes was evidently a worm-like aquatic animal of the Ediacaran. The two clades diverged over 600 million years ago. Protostomes evolved into over a million species alive today, compared to around 73,000 deuterostome species.[6]

Protostomes are divided into the Ecdysozoa (e.g. arthropods, nematodes) and the Spiralia (e.g. molluscs, annelids, platyhelminths, and rotifers). A modern consensus phylogenetic tree for the protostomes is shown below.[7][8][9][10][11][12][excessive citations] Script error: No such module "Clade".

See also

References

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  1. ^ a b c Page Module:Citation/CS1/styles.css has no content.Hejnol, A.; Martindale, M. Q. (2009). "The mouth, the anus, and the blastopore - open questions about questionable openings". In M. J. Telford; D. T. J. Littlewood (eds.). Animal Evolution — Genomes, Fossils, and Trees. pp. 33–40.
  2. ^ Page Module:Citation/CS1/styles.css has no content.Martín-Durán, José M.; Passamaneck, Yale J.; Martindale, Mark Q.; Hejnol, Andreas (2016). "The developmental basis for the recurrent evolution of deuterostomy and protostomy". Nature Ecology & Evolution. 1 (1): 0005. doi:10.1038/s41559-016-0005. PMID 28812551. S2CID 90795.
  3. ^ Page Module:Citation/CS1/styles.css has no content.Hejnol, A.; Obst, M.; Stamatakis, A.; Ott, M.; Rouse, G. W.; Edgecombe, G. D.; et al. (2009). "Assessing the root of bilaterian animals with scalable phylogenomic methods". Proceedings of the Royal Society B: Biological Sciences. 276 (1677): 4261–4270. doi:10.1098/rspb.2009.0896. PMC 2817096. PMID 19759036.
  4. ^ Page Module:Citation/CS1/styles.css has no content.Peters, Kenneth E.; Walters, Clifford C.; Moldowan, J. Michael (2005). The Biomarker Guide: Biomarkers and isotopes in petroleum systems and Earth history. Vol. 2. Cambridge University Press. p. 717. ISBN 978-0-521-83762-0.
  5. ^ Page Module:Citation/CS1/styles.css has no content.Safra, Jacob E. (2003). The New Encyclopædia Britannica, Volume 1; Volume 3. Encyclopædia Britannica. p. 767. ISBN 978-0-85229-961-6.
  6. ^ The Invertebrate tree of life, Giribet & Edgecombe, 2020; p.155
  7. ^ Page Module:Citation/CS1/styles.css has no content.Edgecombe, Gregory D.; Giribet, Gonzalo; Dunn, Casey W.; Hejnol, Andreas; Kristensen, Reinhardt M.; Neves, Ricardo C.; Rouse, Greg W.; Worsaae, Katrine; Sørensen, Martin V. (June 2011). "Higher-level metazoan relationships: recent progress and remaining questions". Organisms, Diversity & Evolution. 11 (2): 151–172. Bibcode:2011ODivE..11..151E. doi:10.1007/s13127-011-0044-4. S2CID 32169826.
  8. ^ Page Module:Citation/CS1/styles.css has no content.Fröbius, Andreas C.; Funch, Peter (2017-04-04). "Rotiferan Hox genes give new insights into the evolution of metazoan bodyplans". Nature Communications. 8 (1): 9. Bibcode:2017NatCo...8....9F. doi:10.1038/s41467-017-00020-w. PMC 5431905. PMID 28377584.
  9. ^ Page Module:Citation/CS1/styles.css has no content.Smith, Martin R.; Ortega-Hernández, Javier (2014). "Hallucigenia's onychophoran-like claws and the case for Tactopoda" (PDF). Nature. 514 (7522): 363–366. Bibcode:2014Natur.514..363S. doi:10.1038/nature13576. PMID 25132546. S2CID 205239797.
  10. ^ Page Module:Citation/CS1/styles.css has no content."Palaeos Metazoa: Ecdysozoa". palaeos.com. Retrieved 2017-09-02.
  11. ^ Page Module:Citation/CS1/styles.css has no content.Yamasaki, Hiroshi; Fujimoto, Shinta; Miyazaki, Katsumi (June 2015). "Phylogenetic position of Loricifera inferred from nearly complete 18S and 28S rRNA gene sequences". Zoological Letters. 1 18. doi:10.1186/s40851-015-0017-0. PMC 4657359. PMID 26605063.
  12. ^ Page Module:Citation/CS1/styles.css has no content.Peterson, Kevin J.; Cotton, James A.; Gehling, James G.; Pisani, Davide (2008-04-27). "The Ediacaran emergence of bilaterians: congruence between the genetic and the geological fossil records". Philosophical Transactions of the Royal Society of London B: Biological Sciences. 363 (1496): 1435–1443. doi:10.1098/rstb.2007.2233. PMC 2614224. PMID 18192191.

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