Biology:Protostome

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Short description: Clade of animals whose mouth develops before the anus

Protostomes
Temporal range: Ediacaran - Recent
Protostomia.jpg
Some protostomes representing the 6 phyla: Mantis religiosa (Arthropoda), Caenorhabditis elegans (Nematoda), Cornu aspersum (Mollusca), Pseudoceros liparus (Platyhelminthes), Lumbricus terrestris (Annelida), Habrotrocha rosa (Rotifera).
Scientific classification e
Domain: Eukaryota
Kingdom: Animalia
Subkingdom: Eumetazoa
Clade: ParaHoxozoa
Clade: Bilateria
Clade: Nephrozoa
(unranked): Protostomia
Grobben, 1908
Superphyla

Protostomia (/ˌprtəˈstmi.ə/) is the clade of animals once thought to be characterized by the formation of the organism's mouth before its anus 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

Diagram comparing protostomes and deuterostomes at three stages of embryonic development
In protostomes, cells divide with spiral cleavage instead of radial cleavage. During gastrulation, the first opening becomes the embryos' mouth while the anus is formed later. Also, the secondary body cavity (shown in blue) forms from tissue that splits away from the rest, instead of by folding in from the gut walls.

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 (lit. second-mouth), the original dent becomes the anus while the gut eventually tunnels through to make another opening, which forms the mouth. The protostomes (from Greek πρωτο- prōto- 'first' + στόμα stóma '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. Many protostomes (the Spiralia clade) undergo spiral cleavage during cell division instead of radial cleavage.[5] Spiral cleavage happens because the cells' division planes are angled to the polar major axis, instead of being parallel or perpendicular to it. Another difference is that 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.[6]

Evolution

The common ancestor of protostomes and deuterostomes was evidently a worm-like aquatic animal of the Ediacaran. The two clades diverged about 600 million years ago. Protostomes evolved into over a million species alive today, compared to ca. 73,000 deuterostome species.[7]

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.[8][9][10][11][12] The timing of clades radiating into newer clades is given in mya (millions of years ago); less certain placements are indicated with dashed lines.[13]

Bilateria

Xenacoelomorpha Proporus sp.png

Nephrozoa
Deuterostomia

Chordata Common carp (white background).jpg

Ambulacraria Portugal 20140812-DSC01434 (21371237591).jpg

Protostomia
Ecdysozoa
Scalidophora

Priapulida Priapulus caudatus 20150625.jpg

Kinorhyncha Pycnophyes zelinkaei.jpg

Nematoida

Nematoda CelegansGoldsteinLabUNC.jpg

Nematomorpha Paragordius tricuspidatus.jpeg

Loricifera Pliciloricus enigmatus.jpg

Panarthropoda

Onychophora Velvet worm.jpg

Tactopoda

Tardigrada Echiniscus L.png

Arthropoda Long nosed weevil edit.jpg

Spiralia
Gnathifera

Rotifera and allies Bdelloid Rotifer (cropped).jpg

Chaetognatha Chaetoblack.png

Platytrochozoa

Platyhelminthes and allies Sorocelis reticulosa.jpg

Lophotrochozoa

Mollusca Grapevinesnail 01.jpg

Annelida and allies Polychaeta (no).JPG

550 mya
580 mya

KimberellaKimberella NT.jpg

610 mya

See also

References

  1. 1.0 1.1 1.2 Hejnol, A.; Martindale, M. Q. (2009). "The mouth, the anus, and the blastopore - open questions about questionable openings". in M. J. Telford. Animal Evolution — Genomes, Fossils, and Trees. pp. 33–40. https://www.researchgate.net/publication/230766195. 
  2. 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. https://qmro.qmul.ac.uk/xmlui/handle/123456789/54816. 
  3. Hejnol, A. 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. PMID 19759036. 
  4. Peters, Kenneth E.; Walters, Clifford C.; Moldowan, J. Michael (2005). The Biomarker Guide: Biomarkers and isotopes in petroleum systems and Earth history. 2. Cambridge University Press. p. 717. ISBN 978-0-521-83762-0. 
  5. Valentine, James W. (July 1997). "Cleavage patterns and the topology of the metazoan tree of life". PNAS (The National Academy of Sciences) 94 (15): 8001–8005. doi:10.1073/pnas.94.15.8001. PMID 9223303. Bibcode1997PNAS...94.8001V. 
  6. Safra, Jacob E. (2003). The New Encyclopædia Britannica, Volume 1; Volume 3. Encyclopædia Britannica. p. 767. ISBN 978-0-85229-961-6. 
  7. The Invertebrate tree of life, Giribet & Edgecombe, 2020; p.155
  8. Edgecombe, Gregory D.; Giribet, Gonzalo; Dunn, Casey W.; Hejnol, Andreas; Kristensen, Reinhardt M.; Neves, Ricardo C.; Rouse, Greg W.; Worsaae, Katrine et al. (June 2011). "Higher-level metazoan relationships: recent progress and remaining questions". Organisms, Diversity & Evolution 11 (2): 151–172. doi:10.1007/s13127-011-0044-4. http://nrs.harvard.edu/urn-3:HUL.InstRepos:27755241. 
  9. 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. doi:10.1038/s41467-017-00020-w. PMID 28377584. Bibcode2017NatCo...8....9F. 
  10. Smith, Martin R.; Ortega-Hernández, Javier (2014). "Hallucigenia's onychophoran-like claws and the case for Tactopoda". Nature 514 (7522): 363–366. doi:10.1038/nature13576. PMID 25132546. Bibcode2014Natur.514..363S. http://dro.dur.ac.uk/19108/1/19108.pdf. 
  11. "Palaeos Metazoa: Ecdysozoa". http://palaeos.com/metazoa/ecdysozoa/ecdysozoa.html. 
  12. 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. PMID 26605063. 
  13. 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. PMID 18192191. 

External links


Wikidata ☰ Q5171 entry