Temporal range: [1]
Trichoplax adhaerens
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Subkingdom: Parazoa
Phylum: Placozoa
Grell, 1971
Type species
Trichoplax adhaerens

Placozoa (/plækəˈzə/, "flat animals"[3]) is a phylum of marine and free-living (non-parasitic) animals.[4][5] They are simple blob-like animals without any body part or organ, and are merely aggregates of cells. Moving in water by ciliary motion, eating food by engulfment, reproducing by fission or budding, placozoans are described as "the simplest animals on Earth."[6] Structural and molecular analyses have supported them as among the most basal animals,[7][8] thus, constituting the most primitive metazoan phylum.[9]

The first known placozoan, Trichoplax adhaerens, was discovered in 1883 by the German zoologist Franz Eilhard Schulze (1840–1921).[10][11] Describing the uniqueness, another German, Karl Gottlieb Grell (1912–1994), erected a new phylum, Placozoa, for it in 1971. Remaining a monotypic phylum for over a century,[12][13] new species began to be added since 2018. So far, three other species have been described, in two distinct classes: Uniplacotomia (Hoilungia hongkongensis in 2018 and Cladtertia collaboinventa in 2022[14]) and Polyplacotomia (Polyplacotoma mediterranea, the most basal, in 2019[15]).

  1. ^ Knaust, Dirk (2021). "A microbialite with its entombed benthic community from the Middle Triassic (Anisian-Ladinian) Muschelkalk Group of Germany". Palaeontographica Abteilung A. 320 (1–3): 1–63. doi:10.1127/pala/2021/0114.
  2. ^ Tessler, Michael; Neumann, Johannes S.; Kamm, Kai; Osigus, Hans-Jürgen; Eshel, Gil; Narechania, Apurva; Burns, John A.; DeSalle, Rob; Schierwater, Bernd (2022-12-08). "Phylogenomics and the first higher taxonomy of Placozoa, an ancient and enigmatic animal phylum". Frontiers in Ecology and Evolution. 10. doi:10.3389/fevo.2022.1016357.
  3. ^ Rüdiger Wehner & Walter Gehring (June 2007). Zoologie (in German) (24th ed.). Stuttgart: Thieme. p. 696.
  4. ^ Kamm, Kai; Schierwater, Bernd; DeSalle, Rob (2019). "Innate immunity in the simplest animals - placozoans". BMC Genomics. 20 (1): 5. doi:10.1186/s12864-018-5377-3. PMC 6321704. PMID 30611207.
  5. ^ Placozoa at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
  6. ^ Pennisi, Elizabeth (2021). "The simplest of slumbers". Science. 374 (6567): 526–529. doi:10.1126/science.acx9444. ISSN 1095-9203. PMID 34709907. S2CID 240154099.
  7. ^ Neumann, Johannes S.; DeSalle, Tessler; DeSalle, Rob; Michael, Bernd (2021). "Modern invertebrate systematics". In Schierwater, Bernd; DeSalle, Rob (eds.). Invertebrate Zoology: A Tree of Life Approach. CRC Press. p. 71. doi:10.1201/9780429159053. ISBN 978-1-4822-3582-1. S2CID 260730525.
  8. ^ Kawashima, Takeshi; Yoshida, Masa-Aki; Miyazawa, Hideyuki; Nakano, Hiroaki; Nakano, Natumi; Sakamoto, Tatsuya; Hamada, Mayuko (2022). "Observing Phylum-Level Metazoan Diversity by Environmental DNA Analysis at the Ushimado Area in the Seto Inland Sea". Zoological Science. 39 (1): 157–165. doi:10.2108/zs210073. ISSN 0289-0003. PMID 35107003. S2CID 246297787.
  9. ^ Schierwater, Bernd; Eitel, Michael (2015), Wanninger, Andreas (ed.), "Placozoa", Evolutionary Developmental Biology of Invertebrates 1, Vienna: Springer Vienna, pp. 107–114, doi:10.1007/978-3-7091-1862-7_5, ISBN 978-3-7091-1861-0, retrieved 2023-06-02
  10. ^ F. E. Schulze "Trichoplax adhaerens n. g., n. s.", Zoologischer Anzeiger (Elsevier, Amsterdam and Jena) 6 (1883), p. 92.
  11. ^ Cite error: The named reference IZ was invoked but never defined (see the help page).
  12. ^ Voigt, O; Collins AG; Pearse VB; Pearse JS; Hadrys H; Ender A (23 November 2004). "Placozoa — no longer a phylum of one". Current Biology. 14 (22): R944–5. doi:10.1016/j.cub.2004.10.036. PMID 15556848. S2CID 11539852.
  13. ^ Eitel, Michael; Osigus, Hans-Jürgen; DeSalle, Rob; Schierwater, Bernd (2 April 2013). "Global Diversity of the Placozoa". PLOS ONE. 8 (4): e57131. Bibcode:2013PLoSO...857131E. doi:10.1371/journal.pone.0057131. PMC 3614897. PMID 23565136.
  14. ^ Cite error: The named reference :2222 was invoked but never defined (see the help page).
  15. ^ Schierwater, Bernd; Kamm, Kai; Herzog, Rebecca; Rolfes, Sarah; Osigus, Hans-Jürgen (2019-03-04). "Polyplacotoma mediterranea is a new ramified placozoan species". Current Biology. 29 (5): R148–R149. doi:10.1016/j.cub.2019.01.068. ISSN 0960-9822. PMID 30836080.

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