Flatworms

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The division of living beings into systematics is a continuous subject of research. Different systematic classifications exist side by side and one after the other. The taxon treated here has become obsolete due to new research or is not part of the group systematics presented in the German-language Wikipedia.

The flatworms (Platyzoa) are a hypothetical taxon of worm-like, invertebrate animals, which was proposed in 1998 by the biologist Thomas Cavalier-Smith in the rank of sub-kingdom (infrakingdom). Depending on the phylogenetic hypothesis, they are located within the Lophotrochozoa or the Spiralia . According to more recent phylogenomic data, the Platyzoa are a paraphyletic assembly of basal groups and thus not justified as a taxon.

features

The Platyzoa have no morphological autapomorphies . They are simply built primeval mouths (protostomia) without a secondary body cavity (coelom). Protonephridia , the simplest excretory organs, are also present in adult animals. Also typical are mobility through cilia sitting on the outside and direct development without larval stages . Most of the species of Platyzoa are very small and can often only be seen with a microscope . Only among the flatworms and the parasitic scratchworms are there species that can reach lengths of half a meter and more.

Systematics

The following groups were included in the Platyzoa: flatworms (Plathelminthes), belly-haired (Gastrotricha), cup animals (Entoprocta or Kamptozoa, including the Cycliophora ) gnathostomulids (Gnathostomulida) Micrognathozoa and Syndermata (common clade from the rotifers and scratch worms ).

According to recent analyzes of the relationships based on the comparison of homologous DNA sequences, the Platyzoa do not form a common clade. It is rather an assembly of the more basal, simply organized Lophotrochozoa. Their apparent togetherness resulted primarily from a methodical artifact, the so-called long-branch attraction .

Individual evidence

  1. ^ T. Cavalier-Smith (1998): A revised six-kingdom system of life. Biological Reviews (of the Cambridge Philosophical Society) 73: 203-266.
  2. ↑ Burda, Hilken & Zrzavý (2008), pp. 88, 95
  3. ↑ Torsten H. Struck, Alexandra R. Wey-Fabrizius, Anja Golombek, Lars Hering, Anne Weigert, Christoph Bleidorn, Sabrina Klebow, Nataliia Iakovenko, Bernhard Hausdorf, Malte Petersen, Patrick Kück, Holger Herlyn, Thomas Hankel (2014): Platyzoan Paraphyly Based on Phylogenomic Data Supports a Noncoelomate Ancestry of Spiralia. Molecular Biology and Evolution 31 (7): 1833-1849. doi : 10.1093 / molbev / msu143
  4. ↑ Anja Golombek, Sarah Tobergte, Torsten H. Struck (2015): Elucidating the phylogenetic position of Gnathostomulida and first mitochondrial genomes of Gnathostomulida, Gastrotricha and Polycladida (Platyhelminthes). Molecular Phylogenetics and Evolution 86: 49-63. doi : 10.1016 / j.ympev.2015.02.013
  5. ↑ Bernhard Egger, François Lapraz, Bartłomiej Tomiczek, Steven Müller, Christophe Dessimoz, Johannes Girstmair, Nives Škunca, Kate A. Rawlinson, Christopher B. Cameron, Elena Beli, M. Antonio Todaro, Mehrez Gammoudi, Carolina Noreña, Maximilian J. Telford (2015): A Transcriptomic-Phylogenomic Analysis of the Evolutionary Relationships of Flatworms. Current Biology 25 (10): 1347-1353. doi : 10.1016 / j.cub.2015.03.034