Xenoturbella

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Xenoturbella
Xenoturbella japonica

Xenoturbella japonica

Systematics
Trunk : Xenacoelomorpha
Sub-stem : Xenoturbellida
Class : not classified
Order : not classified
Family : Xenoturbellidae
Genre : Xenoturbella
Scientific name of the  family
Xenoturbellidae
Bourlat et al., 2006
Scientific name of the  genus
Xenoturbella
Westblad , 1949
species

The Xenoturbella ( Gr . + Lat . Foreign strudelworms ) form a genus of animals within the Bilateria . It is the only genus in the Xenoturbellidae family , which in turn is the only family in the Xenoturbellida sub- strain. The animals , which are only a few centimeters long, live marine on muddy floors; the first animals were found in the Skagerrak in 1915 , but were not described until 1949 .

features

The Xenoturbella are up to 20 cm long. They are characterized by a flattened body with a ventral-side central groove, which is surrounded by cilia (eyelash groove). The mouth opening is also in this channel or in front of it. The animals collected on the American coasts had an epidermal network on the ventral side that has not been described and perhaps overlooked for the European species.

They have a rather simple internal structure. Despite the lack of gonads , the animals develop germ cells and the embryos are stored in follicles. With the exception of one organ of equilibrium (statocyst), the animals have only a few other defined organs . The cavity of the statocyst is equipped with flagella and several statoliths , which, unlike all other known animal groups, are also ciliate and move within the statocyst. Furthermore, the animals have a diffuse nervous system below the epidermis (upper skin), which is also very rich in glands. The only body cavity is an anusless and sac-shaped intestine, there is no secondary body cavity ( coelom ).

Distribution and habitats

The first specimens of the genus were found on the coasts of Sweden , Scotland and Iceland in the shallow water area. In 2016, four new species of the genus were described from the deep sea regions of the American and Mexican Pacific coasts down to depths of over 2500 meters.

Systematics

The genus now contains seven known species of worm-like animals. Since the first description of a specimen found in 1915, which was named Xenoturbella bocki in 1949 , the taxonomic classification of the genus has been controversial. First, the animals found were identified as free-living flatworms . Then they were mistaken for molluscs and then placed with the new mouths . Within the Neumünder they form the tribe Xenacoelomorpha together with the Acoelomorpha . The latest analyzes place the Xenacoelomorpha as a sister group to the remaining Bilateria , which are summarized as Nephrozoa .

Phylogenetic system of the genus Xenoturbella according to Rouse et al. 2016
  Xenoturbella  
  Shallow water species  


 X. bocki


   

 X. bocki (described as X. westbladi )



   

 X. hollandorum



  Deep sea species  

 X. monstrous pink


   

 X. profunda


   

 X. churro





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The previous species that have been assigned to this genus are:

Xenoturbella westbladi was described by Rouse et al. In 2016, due to the great similarities of the genetic material to Xenoturbella bocki, it was not regarded as an independent species and was therefore synonymous with it . The relationship of the previously known species was investigated on the basis of a molecular-biological DNA analysis, according to which X. monstrosa, together with X. profunda and X. churro, forms a common taxon of deep-sea species, which are opposed to the shallow water species X. bocki and X. hollandorum . The species X. japonica , which was first described in 2017/2018, is also counted among the latter .

Individual evidence

  1. ^ A b c d e f Greg W. Rouse, Nerida G. Wilson, Jose I. Carvajal, Robert C. Vrijenhoek: New deep-sea species of Xenoturbella and the position of Xenacoelomorpha. Nature 530, Feb. 4, 2016; Pp. 94-97 doi : 10.1038 / nature16545
  2. ↑ a b Olle Israelsson, Graham E. Budd: Eggs and embryos in Xenoturbella (phylum uncertain) are not ingested prey . In: Development Genes and Evolution. Vol. 215, 2005, pp. 358-363, PMID 15818482
  3. ↑ Karin Sindemark Kronestedt: Sixten Bock. (No longer available online.) April 12, 2012, formerly in the original ; Retrieved January 14, 2013 (Swedish).  ( Page no longer available , search in web archives )@1@ 2Template: Dead Link / www.nrm.se
  4. ↑ wellcome.ac.uk ( Memento from October 9, 2010 in the Internet Archive )
  5. ↑ E. Westblad: Xenoturbella Bocki ng, n.sp., a peculiar primitive turbellarian type . In: Arkiv för Zoologi. Vol. 1, 1949. Pages 3-29
  6. ↑ M. Noren, U. Jondelius: Xenoturbella's molluscan relatives ... in Nature. Vol. 390, 1997, pp. 31-32
  7. ↑ a b S. J. Bourlat, C. Nielsen, AE Lockyer, D. Timothy J. Littlewood, MJ Telford: Xenoturbella is a deuterostome did eats molluscs in Nature. Vol. 424, 2003, pp. 925-928, nature.com
  8. ↑ Hervé Philippe, Henner Brinkmann, Richard R. Copley, Leonid L. Moroz, Hiroaki Nakano, Albert J. Poustka, Andreas Wallberg, Kevin J. Peterson & Maximilian J. Telford: Acoelomorph flatworms are deuterostomes related to Xenoturbella , Nature 470, p 255–258, 10 February 2011, doi: 10.1038 / nature09676
  9. ^ A b Johanna Taylor Cannon, Bruno Cossermelli Vellutini, Julian Smith, Fredrik Ronquist, Ulf Jondelius, Andreas Hejnol: Xenacoelomorpha is the sister group to Nephrozoa. Nature 530, Feb. 4, 2016; Pp. 89-93 doi : 10.1038 / nature16520
  10. ↑ Hiroaki Nakano, Hideyuki Miyazawa, Akiteru Maeno, Toshihiko Shiroishi, Keiichi Kakui, Ryo Koyanagi, Miyuki Kanda, Noriyuki Satoh, Akihito Omori & Hisanori Khotsuka: A new species of Xenoturbella from the western Pacific Ocean and the evolution of Xenoturbella. BMC Evolutionary Biology 17: 245, December 18, 2017; 11 S. doi : 10.1186 / s12862-017-1080-2
  11. ↑ Hiroaki Nakano, Hideyuki Miyazawa, Akiteru Maeno, Toshihiko Shiroishi, Keiichi Kakui, Ryo Koyanagi, Miyuki Kanda, Noriyuki Satoh, Akihito Omori & Hisanori Khotsuka: Correction to: A new species evolution of Xenoturbella from the western Pacific Ocean and the Xenoturbella. BMC Evolutionary Biology 18:83, June 7, 2018; 2 p. Doi : 10.1186 / s12862-018-1190-5