Editing Placozoa (section)

== History ==
''Trichoplax'' was discovered in 1883 by the German zoologist [[Franz Eilhard Schulze]], in a seawater aquarium at the Zoological Institute in [[Graz, Austria]].<ref name=":0" /><ref>{{Cite journal |last1=Schierwater |first1=Bernd |last2=Osigus |first2=Hans-Jürgen |last3=Bergmann |first3=Tjard |last4=Blackstone |first4=Neil W. |last5=Hadrys |first5=Heike |last6=Hauslage |first6=Jens |last7=Humbert |first7=Patrick O. |last8=Kamm |first8=Kai |last9=Kvansakul |first9=Marc |last10=Wysocki |first10=Kathrin |last11=DeSalle |first11=Rob |display-authors=8 |date=2021 |title=The enigmatic Placozoa part 1: Exploring evolutionary controversies and poor ecological knowledge |journal=BioEssays |volume=43 |issue=10 |pages=e2100080 |doi=10.1002/bies.202100080 |pmid=34472126|s2cid=237387715 |doi-access=free }}</ref> The generic name is derived from the classical Greek {{lang|grc|θρίξ}} (''{{lang|grc-Latn|thrix}}''), meaning "hair", and {{lang|grc|πλάξ}} (''{{lang|grc-Latn|plax}}''), "plate". The specific epithet ''adhaerens'' is Latin meaning "adherent", reflecting its propensity to stick to the glass slides and pipettes used in its examination.<ref name=":1">{{Cite journal |last1=Syed |first1=T. |last2=Schierwater |first2=B. |name-list-style= |date=2002 |title=''Trichoplax adhaerens'': discovered as a missing link, forgotten as a hydrozoan, re-discovered as a key to metazoan evolution |url=https://hal.sorbonne-universite.fr/hal-03198912/document |url-status=dead |journal=Vie Milieu |volume=52 |issue=4 |pages=177–187 |via=[[HAL (open archive)|HAL]] |access-date=2023-06-02 |archive-date=2023-06-02 |archive-url=https://web.archive.org/web/20230602072630/https://hal.sorbonne-universite.fr/hal-03198912/document }}</ref> Schulze realized that the animal could not be a member of any existing phyla, and based on the simple structure and behaviour, concluded in 1891 that it must be an early metazoan. He also observed the reproduction by fission, cell layers and locomotion.<ref name=":3">{{Cite journal |last1=Romanova |first1=Daria Y. |last2=Varoqueaux |first2=Frédérique |last3=Daraspe |first3=Jean |last4=Nikitin |first4=Mikhail A. |last5=Eitel |first5=Michael |last6=Fasshauer |first6=Dirk |last7=Moroz |first7=Leonid L. |date=2021 |title=Hidden cell diversity in Placozoa: ultrastructural insights from Hoilungia hongkongensis |journal=Cell and Tissue Research |volume=385 |issue=3 |pages=623–637 |doi=10.1007/s00441-021-03459-y |pmc=8523601 |pmid=33876313}}</ref> 

In 1893, Italian zoologist [[Francesco Saverio Monticelli]] described another animal which he named ''Treptoplax'', the specimens of which he collected from Naples. He gave the species name ''T. reptans'' in 1896.<ref>{{Cite journal |last1=Cattaneo-Vietti |first1=R. |last2=Russo |first2=G. F. |date=2019-01-01 |title=A brief history of the Italian marine biology |journal=The European Zoological Journal |language=en |volume=86 |issue=1 |pages=294–315 |doi=10.1080/24750263.2019.1651911 |s2cid=202372627 |issn=2475-0263|doi-access=free }}</ref> Monticelli did not preserve them and no other specimens were found again, as a result of which the identification is ruled as doubtful, and the species rejected.<ref name=":2">{{Cite journal |last1=Tessler |first1=Michael |last2=Neumann |first2=Johannes S. |last3=Kamm |first3=Kai |last4=Osigus |first4=Hans-Jürgen |last5=Eshel |first5=Gil |last6=Narechania |first6=Apurva |last7=Burns |first7=John A. |last8=DeSalle |first8=Rob |last9=Schierwater |first9=Bernd |date=2022-12-08 |title=Phylogenomics and the first higher taxonomy of Placozoa, an ancient and enigmatic animal phylum |journal=Frontiers in Ecology and Evolution |volume=10 |doi=10.3389/fevo.2022.1016357 |issn=2296-701X |doi-access=free }}</ref><ref>{{Cite web |title=WoRMS - World Register of Marine Species - Treptoplax reptans Monticelli, 1896 |url=https://www.marinespecies.org/aphia.php?p=taxdetails&id=142022 |access-date=2023-06-02 |website=www.marinespecies.org}}</ref>

Schulze's description was opposed by other zoologists. For instance, in 1890, F.C. Noll argued that the animal was a flat worm (Turbellaria).<ref name=":22">{{Cite journal |last1=Tessler |first1=Michael |last2=Neumann |first2=Johannes S. |last3=Kamm |first3=Kai |last4=Osigus |first4=Hans-Jürgen |last5=Eshel |first5=Gil |last6=Narechania |first6=Apurva |last7=Burns |first7=John A. |last8=DeSalle |first8=Rob |last9=Schierwater |first9=Bernd |date=2022-12-08 |title=Phylogenomics and the first higher taxonomy of Placozoa, an ancient and enigmatic animal phylum |journal=Frontiers in Ecology and Evolution |volume=10 |doi=10.3389/fevo.2022.1016357 |issn=2296-701X |doi-access=free }}</ref> In 1907, Thilo Krumbach published a hypothesis that ''Trichoplax'' is not a distinct animal but that it is a form of the planula larva of the [[Sea anemone|anemone]]-like [[hydrozoan]] ''Eleutheria krohni''. Although this was refuted in print by Schulze and others, Krumbach's analysis became the standard textbook explanation, and nothing was printed in zoological journals about ''Trichoplax'' until the 1960s.<ref name=":1" /> 

The development of [[electron microscopy]] in the mid-20th century allowed in-depth observation of the cellular components of organisms, following which there was renewed interest in ''Trichoplax'' starting in 1966.<ref>{{Cite journal |last1=Kuhl |first1=Willi |last2=Kuhl |first2=Gertrud |date=1966 |title=Untersuchungen über das bewegungsverhalten von Trichoplax adhaerens F. E. Schulze (Zeittransformation: Zeitraffung) |url=http://link.springer.com/10.1007/BF00442291 |journal=Zeitschrift für Morphologie und Ökologie der Tiere |language=de |volume=56 |issue=4 |pages=417–435 |doi=10.1007/BF00442291 |s2cid=20206608 |issn=0720-213X}}</ref> The most important descriptions were made by [[Karl Gottlieb Grell]] at the University of Tübingen since 1971.<ref>{{Cite journal |last=Grell |first=K. G. |date=1971 |title=Embryonalentwicklung bei Trichoplax adhaerens F. E. Schulze |url=http://link.springer.com/10.1007/BF00598728 |journal=Die Naturwissenschaften |language=de |volume=58 |issue=11 |pages=570 |bibcode=1971NW.....58..570G |doi=10.1007/BF00598728 |s2cid=40022799 |issn=0028-1042}}</ref><ref>{{Cite journal |last=Grell |first=Karl G. |date=1972 |title=Eibildung und furchung von Trichoplax adhaerens F. E. Schulze (Placozoa) |url=http://link.springer.com/10.1007/BF00391925 |journal=Zeitschrift für Morphologie der Tiere |language=de |volume=73 |issue=4 |pages=297–314 |doi=10.1007/BF00391925 |s2cid=22931046 |issn=0720-213X}}</ref> That year, Grell revived Schulze's interpretation that the animals are unique and created a new phylum Placozoa.<ref>{{Cite journal |last=G |first=Grell K. |date=1971 |title=Trichoplax adhaerens F. E. Schulze und die Entstehung der Metazoen |url=https://cir.nii.ac.jp/crid/1571417125100030080 |journal=Naturwissenschaftliche Rundschau |volume=24 |pages=160–161}}</ref><ref name=":1" /> Grell derived the name from the placula hypothesis, [[Otto Bütschli]]'s notion on the [[Urmetazoan|origin of metazoans]].<ref>{{Cite journal |last1=Schierwater |first1=Bernd |last2=DeSalle |first2=Rob |date=2018 |title=Placozoa |journal=Current Biology |language=en |volume=28 |issue=3 |pages=R97–R98 |doi=10.1016/j.cub.2017.11.042|pmid=29408263 |s2cid=235331464 |doi-access=free |bibcode=2018CBio...28..R97S }}</ref>