Why are plants chordatas

As Newcomers (Deuterostomia) or second mouths are those animals with a symmetrical structure on both sides (bilateria), in which the primal mouth (blastopore) becomes the anus during the embryonic development of the intestine and the mouth breaks through secondarily from the primal intestine (archenteron) (the process is called deuterostomy).

Scientific importance

Deuterostomy was traditionally an important morphological feature in order to bring together groups as diverse as the Chordata, Hemichordata and Echinodermata as a community of descent (see section Systematics). How many bilateral groups are to be classified in the taxon Deuterostomia, however, has long been controversial, since deuterostomies, for example, also occur in arrow worms and some Lophophorata, and also in some string worms and arthropods.

Some clarity has been achieved on this question by means of molecular biological relationship research. Accordingly, Chordata, Hemichordata and Echinodermata actually form a community of descent, but the remaining groups with deuterostomies do not belong to it.


The newcomers include three recent and one extinct animal phyla:

Current phylogenomic work[1][2] result in the following scheme:

What is particularly noticeable about this system is the new Monophylum Olfactores, which combines Tunicata and Craniata. In addition, the Acrania form the sister group. This contradicts the traditional view of comparative morphology, according to which Acrania and Craniata should be combined to form the Monophylum Notochordata. In the current system shown, some common group names are no longer used for various reasons:

  • Ambulacralia - Synonymous with Ambulacraria
  • Cephalochordata - Synonymous with Acrania
  • Chordonia - Synonymous with chordata
  • Coelomorpha - Synonymous with Ambulacraria
  • Craniota - Synonymous with Craniata
  • Euchordata - Synonym for Notochordata
  • Myomerozoa - Synonymous with Notochordata
  • Notochordata - Paraphylum from Acrania and Craniata
  • Notoneuralia - Synonymous with deuterostomia
  • Urochordata - Synonym for Tunicata
  • Vertebrata - Synonymous with Craniata
  • Xenambulacraria - A taxon that should include Ambulacraria and the Xenoturbellida strain.[3] According to other studies, including a recent one, the Xenoturbellida do not seem to belong to the Deuterostomia at all and rather to be relatives of the Acoelomorpha[4]. On the other hand, there are also current studies of their mitochondrial genome, which continue to support the classification as (basal) deuterostomia [5].

See also

Web links

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  1. ↑ Philippe H, Derelle R, Lopez P, Pick K, Borchiellini C, Boury-Esnault N, Vacelet J, Renard E, Houliston E, Quéinnec E, Da Silva C, Wincker P, Le Guyader H, Leys S, Jackson DJ, Schreiber F, Erpenbeck D, Morgenstern, Wörheide G, Manuel M: Phylogenomics Revives Traditional Views on Deep Animal Relationships. In: Current Biology 19 (2009)
  2. ↑ Dunn CW, Hejnol A, Matus DQ, Pang K, Browne WE, Smith SA, Seaver E, Rouse GW, Obst M, Edgecombe GD, Sørensen MV, Haddock SHD, Schmidt-Rhaesa A, Okusu A, Møbjerg Kristensen R, Wheeler WC, Martindale MQ, Giribet G: Broad phylogenomic sampling improves resolution of the animal tree of life. In: Nature 452 (2008): 745-749
  3. ↑ Bourlat SJ, Juliusdottir T, Lowe CJ, Freeman R, Aronowicz J, Kirschner M, Lander ES, Thorndyke M, Nakano H, Kohn AB, Heyland A, Moroz LL, Copley RR, Telford MJ: Deuterostome phylogeny reveals monophyletic chordates and the new phylum Xenoturbellida. In: Nature 444 (2006): 85-88
  4. ↑ Hejnol A, Obst M, Stamatakis A, Ott M, Rouse GW, Edgecombe GD, Martinez P, Baguñà J, Bailly X, Jondelius U, Wiens M, Müller WEG, Seaver E, Wheeler WC, Martindale MQ, Giribet G, Dunn CW: Assessing the root of bilaterian animals with scalable phylogenomic methods. In: Proceedings of The Royal Society B Biological Sciences 276 (2009): 4261-4270
  5. ↑ Bourlat SJ, Rota-Stabelli O, Lanfear R, Telford MJ: The mitochondrial genome structure of Xenoturbella bocki (phylum Xenoturbellida) is ancestral within the deuterostomes in BMC Evolutionary Biology 9: 107 (2009) http://www.biomedcentral.com/content/pdf/1471-2148-9-107.pdf