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From Wikipedia, the free encyclopedia

Fossil range: Ediacaran–Recent
A Caribbean Reef Squid, an example of a protostome.
Scientific classification
Kingdom: Animalia
Subkingdom: Eumetazoa
(unranked): Protostomia
Grobben, 1908

Protostomia (from the Greek: mouth first) are a clade of animals. Together with the deuterostomes and a few smaller phyla, they make up the Bilateria, mostly comprising animals with bilateral symmetry and three germ layers. The major distinctions between deuterostomes and protostomes are found in embryonic development.


In animals at least as complex as earthworms, the embryo forms a dent on one side, the blastopore, which deepens to become the archenteron, the first phase in the growth of the gut. In deuterostomes, the original dent becomes the anus while the gut eventually tunnels through to make another opening, which forms the mouth. The protostomes were so named because it used to be thought that in their embryos the dent formed the mouth while the anus was formed later, at the opening made by the other end of the gut. More recent research, however, shows that in protostomes the edges of the dent close up in the middle, leaving openings at the ends which become the mouth and anus.[1] However, this idea has been challenged, because the platyhelminthes, a group which forms a sister group to the rest of the bilaterian animals, have a single mouth which leads into a blind gut (with no anus). The genes employed in the embryonic construction of this mouth are the same as those expressed around the protostome mouth, [2]

There are other significant differences between the protostome and deuterostome patterns of development:

  • Most protostomes are schizocoelomates, meaning a solid mass of the embryonic mesoderm splits to form a coelom. A few, such as Priapulids, have no coelom, but they may have descended from schizocoelomate ancestors. On the other hand all known deuterostomes are enterocoelous, meaning that the coelom is formed from longitudinal pouches of the archenteron which then become separate cavities.
  • Within the Protostomes a number of phyla undergo what is known as spiral cleavage which is determinate, meaning that the fate of the cells is determined as they are formed. This is in contrast to deuterostomes which have radial cleavage that is indeterminate.

Current molecular data suggest that protostome animals can be divided into three major groups:

as well as a number of minor taxa of basal or ambiguous affinity.

See also


  1. ^ Arendt, D.; Technau, U.; Wittbrodt, J. (4 January 2001). "Evolution of the bilaterian larval foregut". Nature 409: 81–85. doi:10.1038/35051075. Retrieved 2008-07-14. 
  2. ^ Hejnol, A; Martindale, Mq (Nov 2008). "Acoel development indicates the independent evolution of the bilaterian mouth and anus.". Nature 456 (7220): 382–6. doi:10.1038/nature07309. ISSN 0028-0836. PMID 18806777. 


Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary




Greek first + mouth

Proper noun

Wikipedia has an article on:



  1. a taxonomic superphylum, within subkingdom Eumetazoa - the bilateral animals with three germ cells

See also

Wikispecies has information on:



Up to date as of January 23, 2010

From Wikispecies

Nuvola apps important.svg The status, affinity, scope or nomenclature of this taxon is disputed.

Please see discussion on the talk page.


Main Page
Cladus: Eukaryota
Supergroup: Unikonta
Cladus: Opisthokonta
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Cladus: Protostomia
Cladi: Ecdysozoa - Spiralia

Overview of extant phyla (25): Acanthocephala - Annelida - Arthropoda - Brachiopoda - Bryozoa - Cycliophora - Echiura - Entoprocta - Gastrotricha - Gnathostomulida - Kinorhyncha - Loricifera - Micrognathozoa - Mollusca - Myzostomida - Nematoda - Nematomorpha - Nemertea - Onychophora - Phoronida - Platyhelminthes - Priapulida - Rotifera - Sipuncula - Tardigrada




  • Bourlat, S.J.; Nielsen, C.; Economou, A.D.; Telford, M.J. 2008: Testing the new animal phylogeny: a phylum level molecular analysis of the animal kingdom. Molecular phylogenetics and evolution, doi:10.1016/j.ympev.2008.07.008
  • Grobben K. (1908). Die systematische Einteilung des Tierreiches. - Verhandlungen der k.k. zoologisch-botanischen Gesellschaft in Wien.
  • Helmkampf, M.; Bruchhaus, I.; Hausdorf, B. 2008: Multigene analysis of lophophorate and chaetognath phylogenetic relationships. Molecular phylogenetics and evolution, 46: 206-214.
  • Nielsen, C. 2003: Proposing a solution to the Articulata–Ecdysozoa controversy. Zoologica scripta, 32: 475-482.
  • Passamaneck, Y.; Halanych, K.M. 2006: Lophotrochozoan phylogeny assessed with LSU and SSU data: evidence of lophophorate polyphyly. Molecular phylogenetics and evolution, 40: 20–28.

Vernacular names

Български: Първичноустни
Česky: Prvoústí
Deutsch: Urmünder
Ελληνικά: Πρωτοστόμια
English: protostomes
Español: Protóstomos, Protostomados
Esperanto: Prabusulo
Français: Protostomes, Protostomiens
한국어: 선구동물상문
Italiano: Protostomi
Magyar: Ősszájúak
Македонски: Првоусни животни
Nederlands: Oermondigen
日本語: 旧口動物枝 (きゅうこうどうぶつし)
‪Norsk (bokmål)‬: Protostomier
Polski: Pierwouste
Português: Protostómios/Protostômios/Protostomados
Русский: Первичноротые
Suomi: Protostomaatit, Alkusuiset
Svenska: Protostomia
Türkçe: İlkin ağızlılar
中文: 原口动物
Wikimedia Commons For more multimedia, look at Protostomia on Wikimedia Commons.


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