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Xenacoelomorpha

Xenacoelomorpha is a small phylum of bilaterian invertebrate animals, consisting of two sister groups: xenoturbellids and acoelomorphs. This new phylum was named in February 2011 and suggested based on morphological synapomorphies (physical appearances shared by the animals in the clade), which was then confirmed by phylogenomic analyses of molecular data (similarities in the DNA of the animals within the clade).

Xenacoelomorpha
Xenoturbella japonica, a xenacoelomorph member (xenoturbellids)
Proporus sp., another xenacoelomorph member (acoelomorphs)
Scientific classification
Kingdom: Animalia
Subkingdom: Eumetazoa
Clade: ParaHoxozoa
Clade: Bilateria
Phylum: Xenacoelomorpha
Philippe et al. 2011
Subphyla

Contents

The clade (groupings of organisms based on their most recent shared/common ancestors) Xenacoelomorpha groups the Acoelomorpha and the genus Xenoturbella, due to molecular studies. Initially this phylum was considered to be a member of the deuterostomes, (meaning during development, as an embryo, the anus develops first and then the mouth), but because of recent transcriptome analysis, it was concluded that phylum Xenacoelomorpha is the sister group (two closest relatives in a phylogenetic tree) to the Nephrozoa, which includes both the protostomes (where in development of the embryo, the mouth forms first, then the anus) and the deuterostomes, therefore phylum Xenacoelomorpha is the basalmost bilaterian clade. This would mean they are neither a deuterostome nor protostome.

However, some studies point out that their basal placement may be caused by high mutation rates leading to long branch attraction (LBA). These analyses suggest that the xenacoelomorphs are instead the sister group of Ambulacraria forming the clade Xenambulacraria and that despite their simple body plans, they actually derive from a more complex ancestor. Having a larger number of species within this group would allow for better conclusions and analysis to be made within the phylum and in groups closely related to the phylum.

All species within phylum xenacoelomorphs are bilateral, meaning they have a mirror image on their right and left axis, like humans. While they are triploblasts (meaning they have the three germ layers: ectoderm, endoderm, and mesoderm) they do not have a true body cavity (they lack a coelom) because they have an acoelomate body plan. While animals that are diploblastic (only have two germ layers: ectoderm and endoderm) also lack a coelom, they do not have an acoelomate body plan because they lack the mesoderm germ layer. In acoels, the mouth opens directly into a large endodermal syncytium, while in nemertodermatids and xenoturbellids there is a sack-like gut lined by unciliated cells.

The nervous system is basiepidermal, i.e., located right under the epidermis, and a brain is absent. In xenoturbellids it is constituted by a simple nerve net without any special concentration of neurons, while in acoelomorphs it is arranged in a series of longitudinal bundles united in the anterior region by a ring comissure of variable complexity.

The sensory organs include a statocyst (for balance) and some groups have two unicellular ocelli (simple eyes).

The epidermis of all species within the phylum is ciliated. The cilia are composed of a set of 9 pairs of peripheral microtubules and one or two central microtubules (patterns 9+1 and 9+2, respectively). The pairs 4–7 terminate before the tip, creating a structure called a "shelf".

This phylum consists of species that are free-living, parasitic, and symbiotic. They are small flat like worms found in marine and sometimes brackish water environments, on the sediments. They can be found at depths of almost 4 km and near hydrothermal vents. The phylum is hermaphrodite (male and female sex organs) and reproduces sexually with direct development, meaning they skip the vulnerable larval stage.

  1. Tyler, S.; Schilling, S.; Hooge, M.; Bush, L.F. (2006–2016). "Xenacoelomorpha". Turbellarian taxonomic database. Version 1.7. Retrieved3 February 2016.
  2. Philippe, H.; Brinkmann, H.; Copley, R. R.; Moroz, L. L.; Nakano, H.; Poustka, A. J.; Wallberg, A.; Peterson, K. J.; Telford, M. J. (10 February 2011). "Acoelomorph flatworms are deuterostomes related to Xenoturbella". Nature. 470 (7333): 255–258. Bibcode:2011Natur.470..255P. doi:10.1038/nature09676. PMC4025995. PMID 21307940.
  3. Lundin, K (1998). "The epidermal ciliary rootlets of Xenoturbella bocki (Xenoturbellida) revisited: new support for a possible kinship with the Acoelomorpha (Platyhelminthes)". Zoologica Scripta. 27 (3): 263–270. doi:10.1111/j.1463-6409.1998.tb00440.x. S2CID 85324766.
  4. 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. PMC2817096. PMID 19759036.
  5. Perseke, M.; Hankeln, T.; Weich, B.; Fritzsch, G.; Stadler, P.F.; Israelsson, O.; Bernhard, D.; Schlegel, M. (August 2007). "The mitochondrial DNA of Xenoturbella bocki: genomic architecture and phylogenetic analysis"(PDF). Theory Biosci. 126 (1): 35–42. CiteSeerX10.1.1.177.8060. doi:10.1007/s12064-007-0007-7. PMID 18087755. S2CID 17065867.
  6. Cannon, J.T.; Vellutini, B.C.; Smith, J.; Ronquist, F.; Jondelius, U.; Hejnol, A. (4 February 2016). "Xenacoelomorpha is the sister group to Nephrozoa". Nature. 530 (7588): 89–93. Bibcode:2016Natur.530...89C. doi:10.1038/nature16520. PMID 26842059. S2CID 205247296.
  7. Philippe, Hervé; Poustka, Albert J.; Chiodin, Marta; Hoff, Katharina J.; Dessimoz, Christophe; Tomiczek, Bartlomiej; Schiffer, Philipp H.; Müller, Steven; Domman, Daryl; Horn, Matthias; Kuhl, Heiner; Timmermann, Bernd; Satoh, Noriyuki; Hikosaka-Katayama, Tomoe; Nakano, Hiroaki; Rowe, Matthew L.; Elphick, Maurice R.; Thomas-Chollier, Morgane; Hankeln, Thomas; Mertes, Florian; Wallberg, Andreas; Rast, Jonathan P.; Copley, Richard R.; Martinez, Pedro; Telford, Maximilian J. (2019). "Mitigating Anticipated Effects of Systematic Errors Supports Sister-Group Relationship between Xenacoelomorpha and Ambulacraria". Current Biology. 29 (11): 1818–1826.e6. doi:10.1016/j.cub.2019.04.009. hdl:21.11116/0000-0004-DC4B-1. ISSN 0960-9822. PMID 31104936. S2CID 155104811.
  8. Kapli, Paschalia; Telford, Maximilian J. (11 December 2020). "Topology-dependent asymmetry in systematic errors affects phylogenetic placement of Ctenophora and Xenacoelomorpha". Science Advances. 6 (10): eabc5162. doi:10.1126/sciadv.abc5162. PMC7732190. PMID 33310849.
  9. Achatz, Johannes G.; Chiodin, Marta; Salvenmoser, Willi; Tyler, Seth; Martinez, Pedro (June 2013). "The Acoela: on their kind and kinships, especially with nemertodermatids and xenoturbellids (Bilateria incertae sedis)". Organisms Diversity & Evolution. 13 (2): 267–286. doi:10.1007/s13127-012-0112-4. ISSN 1439-6092. PMC3789126. PMID 24098090.
  10. Perea-Atienza, E.; Gavilan, B.; Chiodin, M.; Abril, J. F.; Hoff, K. J.; Poustka, A. J.; Martinez, P. (2015). "The nervous system of Xenacoelomorpha: a genomic perspective". Journal of Experimental Biology. 218 (4): 618–628. doi:10.1242/jeb.110379. ISSN 0022-0949. PMID 25696825.
  11. Franzen, Ake; Afzelius, Bjorn A. (January 1987). "The ciliated epidermis of Xenoturbella bocki (Platyhelminthes, Xenoturbellida) with some phylogenetic considerations". Zoologica Scripta. 16 (1): 9–17. doi:10.1111/j.1463-6409.1987.tb00046.x. ISSN 0300-3256. S2CID 85675105.

Xenacoelomorpha
Xenacoelomorpha Language Watch Edit Xenacoelomorpha 2 ˌ z ɛ n e ˌ s ɛ l oʊ ˈ m ɔːr f e is a small phylum of bilaterian invertebrate animals consisting of two sister groups xenoturbellids and acoelomorphs This new phylum was named in February 2011 and suggested based on morphological synapomorphies physical appearances shared by the animals in the clade 3 which was then confirmed by phylogenomic analyses of molecular data similarities in the DNA of the animals within the clade 2 4 XenacoelomorphaXenoturbella japonica a xenacoelomorph member xenoturbellids Proporus sp another xenacoelomorph member acoelomorphs Scientific classificationKingdom AnimaliaSubkingdom EumetazoaClade ParaHoxozoaClade BilateriaPhylum Xenacoelomorpha Philippe et al 2011 1 SubphylaXenoturbellida Acoelomorpha Contents 1 Phylogenetics 2 Characteristics 3 See also 4 ReferencesPhylogenetics EditThe clade groupings of organisms based on their most recent shared common ancestors Xenacoelomorpha groups the Acoelomorpha and the genus Xenoturbella due to molecular studies 4 Initially this phylum was considered to be a member of the deuterostomes 2 meaning during development as an embryo the anus develops first and then the mouth but because of recent transcriptome analysis it was concluded that phylum Xenacoelomorpha is the sister group two closest relatives in a phylogenetic tree to the Nephrozoa which includes both the protostomes where in development of the embryo the mouth forms first then the anus and the deuterostomes therefore phylum Xenacoelomorpha is the basalmost bilaterian clade 5 6 This would mean they are neither a deuterostome nor protostome However some studies point out that their basal placement may be caused by high mutation rates leading to long branch attraction LBA These analyses suggest that the xenacoelomorphs are instead the sister group of Ambulacraria forming the clade Xenambulacraria and that despite their simple body plans they actually derive from a more complex ancestor 7 8 Having a larger number of species within this group would allow for better conclusions and analysis to be made within the phylum and in groups closely related to the phylum Characteristics EditAll species within phylum xenacoelomorphs are bilateral meaning they have a mirror image on their right and left axis like humans While they are triploblasts meaning they have the three germ layers ectoderm endoderm and mesoderm they do not have a true body cavity they lack a coelom because they have an acoelomate body plan While animals that are diploblastic only have two germ layers ectoderm and endoderm also lack a coelom they do not have an acoelomate body plan because they lack the mesoderm germ layer In acoels the mouth opens directly into a large endodermal syncytium while in nemertodermatids and xenoturbellids there is a sack like gut lined by unciliated cells 9 The nervous system is basiepidermal i e located right under the epidermis and a brain is absent In xenoturbellids it is constituted by a simple nerve net without any special concentration of neurons while in acoelomorphs it is arranged in a series of longitudinal bundles united in the anterior region by a ring comissure of variable complexity 10 The sensory organs include a statocyst for balance and some groups have two unicellular ocelli simple eyes 9 10 The epidermis of all species within the phylum is ciliated The cilia are composed of a set of 9 pairs of peripheral microtubules and one or two central microtubules patterns 9 1 and 9 2 respectively The pairs 4 7 terminate before the tip creating a structure called a shelf 11 This phylum consists of species that are free living parasitic and symbiotic They are small flat like worms found in marine and sometimes brackish water environments on the sediments They can be found at depths of almost 4 km and near hydrothermal vents The phylum is hermaphrodite male and female sex organs and reproduces sexually with direct development meaning they skip the vulnerable larval stage See also EditList of bilaterial animal ordersReferences Edit Tyler S Schilling S Hooge M Bush L F 2006 2016 Xenacoelomorpha Turbellarian taxonomic database Version 1 7 Retrieved 3 February 2016 a b c Philippe H Brinkmann H Copley R R Moroz L L Nakano H Poustka A J Wallberg A Peterson K J Telford M J 10 February 2011 Acoelomorph flatworms are deuterostomes related to Xenoturbella Nature 470 7333 255 258 Bibcode 2011Natur 470 255P doi 10 1038 nature09676 PMC 4025995 PMID 21307940 Lundin K 1998 The epidermal ciliary rootlets of Xenoturbella bocki Xenoturbellida revisited new support for a possible kinship with the Acoelomorpha Platyhelminthes Zoologica Scripta 27 3 263 270 doi 10 1111 j 1463 6409 1998 tb00440 x S2CID 85324766 a b 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 Perseke M Hankeln T Weich B Fritzsch G Stadler P F Israelsson O Bernhard D Schlegel M August 2007 The mitochondrial DNA of Xenoturbella bocki genomic architecture and phylogenetic analysis PDF Theory Biosci 126 1 35 42 CiteSeerX 10 1 1 177 8060 doi 10 1007 s12064 007 0007 7 PMID 18087755 S2CID 17065867 Cannon J T Vellutini B C Smith J Ronquist F Jondelius U Hejnol A 4 February 2016 Xenacoelomorpha is the sister group to Nephrozoa Nature 530 7588 89 93 Bibcode 2016Natur 530 89C doi 10 1038 nature16520 PMID 26842059 S2CID 205247296 Philippe Herve Poustka Albert J Chiodin Marta Hoff Katharina J Dessimoz Christophe Tomiczek Bartlomiej Schiffer Philipp H Muller Steven Domman Daryl Horn Matthias Kuhl Heiner Timmermann Bernd Satoh Noriyuki Hikosaka Katayama Tomoe Nakano Hiroaki Rowe Matthew L Elphick Maurice R Thomas Chollier Morgane Hankeln Thomas Mertes Florian Wallberg Andreas Rast Jonathan P Copley Richard R Martinez Pedro Telford Maximilian J 2019 Mitigating Anticipated Effects of Systematic Errors Supports Sister Group Relationship between Xenacoelomorpha and Ambulacraria Current Biology 29 11 1818 1826 e6 doi 10 1016 j cub 2019 04 009 hdl 21 11116 0000 0004 DC4B 1 ISSN 0960 9822 PMID 31104936 S2CID 155104811 Kapli Paschalia Telford Maximilian J 11 December 2020 Topology dependent asymmetry in systematic errors affects phylogenetic placement of Ctenophora and Xenacoelomorpha Science Advances 6 10 eabc5162 doi 10 1126 sciadv abc5162 PMC 7732190 PMID 33310849 a b Achatz Johannes G Chiodin Marta Salvenmoser Willi Tyler Seth Martinez Pedro June 2013 The Acoela on their kind and kinships especially with nemertodermatids and xenoturbellids Bilateria incertae sedis Organisms Diversity amp Evolution 13 2 267 286 doi 10 1007 s13127 012 0112 4 ISSN 1439 6092 PMC 3789126 PMID 24098090 a b Perea Atienza E Gavilan B Chiodin M Abril J F Hoff K J Poustka A J Martinez P 2015 The nervous system of Xenacoelomorpha a genomic perspective Journal of Experimental Biology 218 4 618 628 doi 10 1242 jeb 110379 ISSN 0022 0949 PMID 25696825 Franzen Ake Afzelius Bjorn A January 1987 The ciliated epidermis of Xenoturbella bocki Platyhelminthes Xenoturbellida with some phylogenetic considerations Zoologica Scripta 16 1 9 17 doi 10 1111 j 1463 6409 1987 tb00046 x ISSN 0300 3256 S2CID 85675105 Retrieved from https en wikipedia org w index php title Xenacoelomorpha amp oldid 1038301259, wikipedia, wiki, book,

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