Jump to content

Placozoa

From Wikipedia, the free encyclopedia
(Redirected from Placozoans)

Placozoans
Temporal range: Middle Triassic–Recent [1]
Trichoplax adhaerens
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Subkingdom: Eumetazoa
Clade: ParaHoxozoa
Phylum: Placozoa
Grell, 1971
Type species
Trichoplax adhaerens
Classes[2]

Placozoa (/ˌplækəˈzoʊə/ PLAK-ə-ZOH-ə; lit. 'flat animals')[3] is a phylum of marine and free-living (non-parasitic) animals.[4][5] They are blob-like animals composed of aggregations 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 a 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 extant 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]). A single putative fossil species is known, the Middle Triassic Maculicorpus microbialis.[1]

History

[edit]

Trichoplax was discovered in 1883 by the German zoologist Franz Eilhard Schulze, in a seawater aquarium at the Zoological Institute in Graz, Austria.[10][16] The generic name is derived from the classical Greek θρίξ (thrix), meaning "hair", and πλάξ (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.[17] 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.[18]

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.[19] 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.[20][21]

Schulze's description was opposed by other zoologists. For instance, in 1890, F.C. Noll argued that the animal was a flat worm (Turbellaria).[22] 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 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.[17]

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.[23] The most important descriptions were made by Karl Gottlieb Grell at the University of Tübingen since 1971.[24][25] That year, Grell revived Schulze's interpretation that the animals are unique and created a new phylum Placozoa.[26][17] Grell derived the name from the placula hypothesis, Otto Bütschli's notion on the origin of metazoans.[27]

Biology

[edit]
Trichoplax body structure in cross section
1 - lipid drop, 2 - cilium, 3 - dorsal layer of cells, 4 - vacuole,
5 - fibrous syncytium, 6 - glandular cell, 7 - vacuole,
8 - ventral layer of cells, 9 - zones of intercellular contacts
Main article: Trichoplax

Placozoans do not have well-defined body plans, much like amoebas, unicellular eukaryotes. As Andrew Masterson reported: "they are as close as it is possible to get to being simply a little living blob."[28] An individual body measures about 0.55 mm in diameter.[29] There are no body parts; as one of the researchers Michael Eitel described: "There's no mouth, there's no back, no nerve cells, nothing."[30] Animals studied in laboratories have bodies consisting of everything from hundreds to millions of cells.[31]

Placozoans have only three anatomical parts as tissue layers inside its body: the upper, intermediate (middle) and lower epithelia. There are at least six different cell types.[32] The upper epithelium is the thinnest portion and essentially comprises flat cells with their cell body hanging underneath the surface, and each cell having a cilium.[33] Crystal cells are sparsely distributed near the marginal edge. A few cells have unusually large number of mitochondria.[32] The middle layer is the thickest made up of numerous fiber cells, which contain mitochondrial complexes, vacuoles and endosymbiotic bacteria in the endoplasmic reticulum. The lower epithelium consists of numerous monociliated cylinder cells along with a few endocrine-like gland cells and lipophil cells. Each lipophil cell contains numerous middle-sized granules, one of which is a secretory granule.[34][33]

The body axes of Hoilungia and Trichoplax are overtly similar to the oral–aboral axis of cnidarians,[35] animals from another phylum with which they are most closely related.[36] Structurally, they can not be distinguished from other placozoans, so that identification is purely on genetic (mitochondrial DNA) differences.[37] Genome sequencing has shown that each species has a set of unique genes and several uniquely missing genes.[14]

Trichoplax is a small, flattened, animal around 1 mm (0.039 in) across. An amorphous multi-celled body, analogous to a single-celled amoeba, it has no regular outline, although the lower surface is somewhat concave, and the upper surface is always flattened. The body consists of an outer layer of simple epithelium enclosing a loose sheet of stellate cells resembling the mesenchyme of some more complex animals. The epithelial cells bear cilia, which the animal uses to help it creep along the seafloor.[11]

The lower surface engulfs small particles of organic detritus, on which the animal feeds. All placozoans can reproduce asexually, budding off smaller individuals, and the lower surface may also bud off eggs into the mesenchyme.[11] Sexual reproduction has been reported to occur in one clade of placozoans,[38][39] whose strain H8 was later found to belong to genus Cladtertia,[2] where intergenic recombination was observed as well as other hallmarks of sexual reproduction.

Some Trichoplax species contain Rickettsiales bacteria as endosymbionts.[40] One of the at least 20 described species turned out to have two bacterial endosymbionts; Grellia which lives in the animal's endoplasmic reticulum and is assumed to play a role in the protein and membrane production. The other endosymbiont is the first described Margulisbacteria, that lives inside cells used for algal digestion. It appears to eat the fats and other lipids of the algae and provide its host with vitamins and amino acids in return.[41] [42]

Studies suggest that aragonite crystals in crystal cells have the same function as statoliths, allowing it to use gravity for spatial orientation.[43]

Located in the dorsal epithelium there are lipid granules called shiny spheres which release a cocktail of venoms and toxins as an anti-predator defense, and can induce paralysis or death in some predators. Genes has been found in Trichoplax with a strong resemblance to the venom genes of some poisonous snakes, like the American copperhead and the West African carpet viper.[44][45]

Global distribution [46]

The Placozoa show substantial evolutionary radiation in regard to sodium channels, of which they have 5–7 different types, more than any other invertebrate species studied to date.[47]

Three modes of population dynamics depended upon feeding sources, including induction of social behaviors, morphogenesis, and reproductive strategies. [48]

In addition to fission, representatives of all species produced “swarmers” (a separate vegetative reproduction stage), which could also be formed from the lower epithelium with greater cell-type diversity.[49]

Evolutionary relationships

[edit]

There is no convincing fossil record of the Placozoa, although the Ediacaran biota (Precambrian, 550 million years ago) organism Dickinsonia appears somewhat similar to placozoans.[50] Knaust (2021) reported preservation of placozoan fossils in a microbialite bed from the Middle Triassic Muschelkalk (Germany).[1]

Traditionally, classification was based on their level of organization, i.e., they possess no tissues or organs. However this may be as a result of secondary loss and thus is inadequate to exclude them from relationships with more complex animals. More recent work has attempted to classify them based on the DNA sequences in their genome; this has placed the phylum between the sponges and the Eumetazoa.[51] In such a feature-poor phylum, molecular data are considered to provide the most reliable approximation of the placozoans' phylogeny.

Their exact position on the phylogenetic tree would give important information about the origin of neurons and muscles. If the absence of these features is an original trait of the Placozoa, it would mean that a nervous system and muscles evolved three times should placozoans and cnidarians be a sister group; once in the Ctenophora, once in the Cnidaria and once in the Bilateria. If they branched off before the Cnidaria and Bilateria split, the neurons and muscles would have the same origin in the two latter groups.

Functional-morphology hypothesis

[edit]
The Placozoa descending side by side with the sponges, cnidarians and ctenophores from a gallertoid by processes of differentiation
A placozoan is a small, flattened animal, typically about one mm across and about 25 μm thick. Like the amoebae they superficially resemble, they continually change their external shape. In addition, spherical phases occasionally form which may facilitate movement. Trichoplax lacks tissues and organs. There is no manifest body symmetry, so it is not possible to distinguish anterior from posterior or left from right. It is made up of a few thousand cells of six types in three distinct layers.[52]

On the basis of their simple structure, the Placozoa were frequently viewed as a model organism for the transition from unicellular organisms to the multicellular animals (Metazoa) and are thus considered a sister taxon to all other metazoans:

Metazoa

Placozoa

Sponges (Porifera)

Animals with tissues (Eumetazoa)

According to a functional-morphology model, all or most animals are descended from a gallertoid, a free-living (pelagic) sphere in seawater, consisting of a single ciliated layer of cells supported by a thin, noncellular separating layer, the basal lamina. The interior of the sphere is filled with contractile fibrous cells and a gelatinous extracellular matrix. Both the modern Placozoa and all other animals then descended from this multicellular beginning stage via two different processes:[53]

  • Infolding of the epithelium led to the formation of an internal system of ducts and thus to the development of a modified gallertoid from which the sponges (Porifera), Cnidaria and Ctenophora subsequently developed.
  • Other gallertoids, according to this model, made the transition over time to a benthic mode of life; that is, their habitat has shifted from the open ocean to the floor (benthic zone). This results naturally in a selective advantage for flattening of the body, as of course can be seen in many benthic species.
Crawling motility and food uptake by Trichoplax adhaerens

While the probability of encountering food, potential sexual partners, or predators is the same in all directions for animals floating freely in the water, there is a clear difference on the seafloor between the functions useful on body sides facing toward and away from the substrate, leading their sensory, defensive, and food-gathering cells to differentiate and orient according to the vertical – the direction perpendicular to the substrate. In the proposed functional-morphology model, the Placozoa, and possibly several similar organisms only known from the fossils, are descended from such a life form, which is now termed placuloid.

Three different life strategies have accordingly led to three different possible lines of development:

  1. Animals that live interstitially in the sand of the ocean floor were responsible for the fossil crawling traces that are considered the earliest evidence of animals; and are detectable even prior to the dawn of the Ediacaran Period in geology. These are usually attributed to bilaterally symmetrical worms, but the hypothesis presented here views animals derived from placuloids, and thus close relatives of Trichoplax adhaerens, to be the producers of the traces.
  2. Animals that incorporated algae as photosynthetically active endosymbionts, i.e. primarily obtaining their nutrients from their partners in symbiosis, were accordingly responsible for the mysterious creatures of the Ediacara fauna that are not assigned to any modern animal taxon and lived during the Ediacaran Period, before the start of the Paleozoic. However, recent work has shown that some of the Ediacaran assemblages (e.g. Mistaken Point) were in deep water, below the photic zone, and hence those individuals could not dependent on endosymbiotic photosynthesisers.
  3. Animals that grazed on algal mats would ultimately have been the direct ancestors of the Placozoa. The advantages of an amoeboid multiplicity of shapes thus allowed a previously present basal lamina and a gelatinous extracellular matrix to be lost secondarily. Pronounced differentiation between the surface facing the substrate (ventral) and the surface facing away from it (dorsal) accordingly led to the physiologically distinct cell layers of Trichoplax adhaerens that can still be seen today. Consequently, these are analogous, but not homologous, to ectoderm and endoderm – the "external" and "internal" cell layers in eumetazoans – i.e. the structures corresponding functionally to one another have, according to the proposed hypothesis, no common evolutionary origin.

Should any of the analyses presented above turn out to be correct, Trichoplax adhaerens would be the oldest branch of the multicellular animals, and a relic of the Ediacaran fauna, or even the pre-Ediacara fauna. Although very successful in their ecological niche, due to the absence of extracellular matrix and basal lamina, the development potential of these animals was of course limited, which would explain the low rate of evolution of their phenotype (their outward form as adults) – referred to as bradytely.[citation needed]

This hypothesis was supported by a recent analysis of the Trichoplax adhaerens mitochondrial genome in comparison to those of other animals.[54] The hypothesis was, however, rejected in a statistical analysis of the Trichoplax adhaerens whole genome sequence in comparison to the whole genome sequences of six other animals and two related non-animal species, but only at the p = 0.07 level, which indicates a marginal level of statistical significance.[51]

Epitheliozoa hypothesis

[edit]

A concept based on purely morphological characteristics pictures the Placozoa as the nearest relative of the animals with true tissues (Eumetazoa). The taxon they share, called the Epitheliozoa, is itself construed to be a sister group to the sponges (Porifera):

  Metazoa  

  Porifera

  Epitheliozoa  
     

  Placozoa

  Eumetazoa

The above view could be correct, although there is some evidence that the ctenophores, traditionally seen as Eumetazoa, may be the sister to all other animals.[55] This is now a disputed classification.[56] Placozoans are estimated to have emerged 750–800 million years ago, and the first modern neuron to have originated in the common ancestor of cnidarians and bilaterians about 650 million years ago (many of the genes expressed in modern neurons are absent in ctenopheres, although some of these missing genes are present in placozoans).[57][58]

The principal support for such a relationship comes from special cell to cell junctions – belt desmosomes – that occur not just in the Placozoa but in all animals except the sponges: They enable the cells to join together in an unbroken layer like the epitheloid of the Placozoa. Trichoplax adhaerens also shares the ventral gland cells with most eumetazoans. Both characteristics can be considered evolutionarily derived features (apomorphies), and thus form the basis of a common taxon for all animals that possess them.[citation needed]

One possible scenario inspired by the proposed hypothesis starts with the idea that the monociliated cells of the epitheloid in Trichoplax adhaerens evolved by reduction of the collars in the collar cells (choanocytes) of sponges as the hypothesized ancestors of the Placozoa abandoned a filtering mode of life. The epitheloid would then have served as the precursor to the true epithelial tissue of the eumetazoans.[citation needed]

In contrast to the model based on functional morphology described earlier, in the Epitheliozoa hypothesis, the ventral and dorsal cell layers of the Placozoa are homologs of endoderm and ectoderm — the two basic embryonic cell layers of the eumetazoans. The digestive gastrodermis in the Cnidaria or the gut epithelium in the bilaterally symmetrical animals (Bilateria) may have developed from endoderm, whereas ectoderm is the precursor to the external skin layer (epidermis), among other things. The interior space pervaded by a fiber syncytium in the Placozoa would then correspond to connective tissue in the other animals. It is unclear whether the calcium ions stored in the syncytium would be related to the lime skeletons of many cnidarians.[citation needed]

As noted above, this hypothesis was supported in a statistical analysis of the Trichoplax adhaerens whole genome sequence, as compared to the whole-genome sequences of six other animals and two related non-animal species.[51]

Eumetazoa hypothesis

[edit]

A third hypothesis, based primarily on molecular genetics, views the Placozoa as highly simplified eumetazoans. According to this, Trichoplax adhaerens is descended from considerably more complex animals that already had muscles and nerve tissues. Both tissue types, as well as the basal lamina of the epithelium, were accordingly lost more recently by radical secondary simplification.[59]

Various studies in this regard so far yield differing results for identifying the exact sister group: In one case, the Placozoa would qualify as the nearest relatives of the Cnidaria, while in another they would be a sister group to the Ctenophora, and occasionally they are placed directly next to the Bilateria. Currently, they are typically placed according to the cladogram below:[60]

  Metazoa  
  
  

In this cladogram the Epitheliozoa and Eumetazoa are synonyms to each other and to the Diploblasts, and the Ctenophora are basal to them.

An argument raised against the proposed scenario is that it leaves morphological features of the animals completely out of consideration. The extreme degree of simplification that would have to be postulated for the Placozoa in this model, moreover, is only known for parasitic organisms, but would be difficult to explain functionally in a free-living species like Trichoplax adhaerens.[citation needed]

This version is supported by statistical analysis of the Trichoplax adhaerens whole genome sequence in comparison to the whole genome sequences of six other animals and two related non-animal species. However, Ctenophora was not included in the analyses, placing the placozoans outside of the sampled Eumetazoans.[51][61]

Cnidaria-sister hypothesis

[edit]

DNA comparisons suggest that placozoans are related to Cnidaria, derived from planula larva (as seen in some Cnidaria).[62] The Bilateria also are thought to be derived from planuloids.[63][64][65][66][67][68][69][70] The Cnidaria and Placozoa body axis are overtly similar, and placozoan and cnidarian cells are responsive to the same neuropeptide antibodies despite extant placozoans not developing any neurons.[71][72]

  Choanozoa  

 Choanoflagellata

  Animalia  

 Porifera

  Eumetazoa  

 Ctenophora

  
  ParaHoxozoa  
     
     

 Placozoa

 Cnidaria

 Bilateria / Triploblasts

680 mya
760 mya
  
950 mya
  
  

References

[edit]
  1. ^ a b c Knaust, Dirk (2021-10-07). "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. ISSN 0375-0442.
  2. ^ a b 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. Bibcode:2021Sci...374..526P. 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. ^ a b F. E. Schulze "Trichoplax adhaerens n. g., n. s.", Zoologischer Anzeiger (Elsevier, Amsterdam and Jena) 6 (1883), p. 92.
  11. ^ a b c Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia: Holt-Saunders International. pp. 84–85. ISBN 978-0-03-056747-6.
  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. Bibcode:2004CBio...14.R944V. 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. ^ a b 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. ISSN 2296-701X.
  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. Bibcode:2019CBio...29.R148O. doi:10.1016/j.cub.2019.01.068. ISSN 0960-9822. PMID 30836080.
  16. ^ Schierwater, Bernd; Osigus, Hans-Jürgen; Bergmann, Tjard; Blackstone, Neil W.; Hadrys, Heike; Hauslage, Jens; Humbert, Patrick O.; Kamm, Kai; et al. (2021). "The enigmatic Placozoa part 1: Exploring evolutionary controversies and poor ecological knowledge". BioEssays. 43 (10): e2100080. doi:10.1002/bies.202100080. PMID 34472126. S2CID 237387715.
  17. ^ a b c Syed, T.; Schierwater, B. (2002). "Trichoplax adhaerens: discovered as a missing link, forgotten as a hydrozoan, re-discovered as a key to metazoan evolution". Vie Milieu. 52 (4): 177–187. Archived from the original on 2023-06-02. Retrieved 2023-06-02 – via HAL.
  18. ^ Romanova, Daria Y.; Varoqueaux, Frédérique; Daraspe, Jean; Nikitin, Mikhail A.; Eitel, Michael; Fasshauer, Dirk; Moroz, Leonid L. (2021). "Hidden cell diversity in Placozoa: ultrastructural insights from Hoilungia hongkongensis". Cell and Tissue Research. 385 (3): 623–637. doi:10.1007/s00441-021-03459-y. PMC 8523601. PMID 33876313.
  19. ^ Cattaneo-Vietti, R.; Russo, G. F. (2019-01-01). "A brief history of the Italian marine biology". The European Zoological Journal. 86 (1): 294–315. doi:10.1080/24750263.2019.1651911. ISSN 2475-0263. S2CID 202372627.
  20. ^ 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. ISSN 2296-701X.
  21. ^ "WoRMS - World Register of Marine Species - Treptoplax reptans Monticelli, 1896". www.marinespecies.org. Retrieved 2023-06-02.
  22. ^ 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. ISSN 2296-701X.
  23. ^ Kuhl, Willi; Kuhl, Gertrud (1966). "Untersuchungen über das bewegungsverhalten von Trichoplax adhaerens F. E. Schulze (Zeittransformation: Zeitraffung)". Zeitschrift für Morphologie und Ökologie der Tiere (in German). 56 (4): 417–435. doi:10.1007/BF00442291. ISSN 0720-213X. S2CID 20206608.
  24. ^ Grell, K. G. (1971). "Embryonalentwicklung bei Trichoplax adhaerens F. E. Schulze". Die Naturwissenschaften (in German). 58 (11): 570. Bibcode:1971NW.....58..570G. doi:10.1007/BF00598728. ISSN 0028-1042. S2CID 40022799.
  25. ^ Grell, Karl G. (1972). "Eibildung und furchung von Trichoplax adhaerens F. E. Schulze (Placozoa)". Zeitschrift für Morphologie der Tiere (in German). 73 (4): 297–314. doi:10.1007/BF00391925. ISSN 0720-213X. S2CID 22931046.
  26. ^ G, Grell K. (1971). "Trichoplax adhaerens F. E. Schulze und die Entstehung der Metazoen". Naturwissenschaftliche Rundschau. 24: 160–161.
  27. ^ Schierwater, Bernd; DeSalle, Rob (2018). "Placozoa". Current Biology. 28 (3): R97–R98. Bibcode:2018CBio...28..R97S. doi:10.1016/j.cub.2017.11.042. PMID 29408263. S2CID 235331464.
  28. ^ Masterson, Andrew (2018-08-01). "Simple organisms not so simple, after all". Cosmos Magazine. Retrieved 2023-06-02.
  29. ^ Eitel, Michael; Francis, Warren R.; Varoqueaux, Frédérique; Daraspe, Jean; Osigus, Hans-Jürgen; Krebs, Stefan; Vargas, Sergio; Blum, Helmut; et al. (2018). "Comparative genomics and the nature of placozoan species". PLOS Biology. 16 (7): e2005359. doi:10.1371/journal.pbio.2005359. PMC 6067683. PMID 30063702.
  30. ^ Wood, Charlie (2018-10-06). "Simplest Animal Reveals Hidden Diversity". Scientific American. Retrieved 2023-06-02 – via Quanta Magazine.
  31. ^ Stanford researchers reveal a new mechanism for how animal cells stay intact
  32. ^ a b Romanova, Daria Y.; Varoqueaux, Frédérique; Daraspe, Jean; Nikitin, Mikhail A.; Eitel, Michael; Fasshauer, Dirk; Moroz, Leonid L. (2021). "Hidden cell diversity in Placozoa: ultrastructural insights from Hoilungia hongkongensis". Cell and Tissue Research. 385 (3): 623–637. doi:10.1007/s00441-021-03459-y. PMC 8523601. PMID 33876313.
  33. ^ a b Eitel, Michael; Francis, Warren R.; Varoqueaux, Frédérique; Daraspe, Jean; Osigus, Hans-Jürgen; Krebs, Stefan; Vargas, Sergio; Blum, Helmut; et al. (2018). "Comparative genomics and the nature of placozoan species". PLOS Biology. 16 (7): e2005359. doi:10.1371/journal.pbio.2005359. PMC 6067683. PMID 30063702.
  34. ^ 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. ISSN 2296-701X.
  35. ^ DuBuc TQ, Ryan JF, Martindale MQ (May 2019). ""Dorsal-Ventral" Genes Are Part of an Ancient Axial Patterning System: Evidence from Trichoplax adhaerens (Placozoa)". Molecular Biology and Evolution. 36 (5): 966–973. doi:10.1093/molbev/msz025. PMC 6501881. PMID 30726986.
  36. ^ Laumer, Christopher E.; Fernández, Rosa; Lemer, Sarah; Combosch, David; Kocot, Kevin M.; Riesgo, Ana; Andrade, Sónia C. S.; Sterrer, Wolfgang; Sørensen, Martin V.; Giribet, Gonzalo (2019-07-10). "Revisiting metazoan phylogeny with genomic sampling of all phyla". Proceedings. Biological Sciences. 286 (1906): 20190831. doi:10.1098/rspb.2019.0831. ISSN 1471-2954. PMC 6650721. PMID 31288696.
  37. ^ Eitel, Michael; Francis, Warren R.; Varoqueaux, Frédérique; Daraspe, Jean; Osigus, Hans-Jürgen; Krebs, Stefan; Vargas, Sergio; Blum, Helmut; et al. (2018). "Comparative genomics and the nature of placozoan species". PLOS Biology. 16 (7): e2005359. doi:10.1371/journal.pbio.2005359. PMC 6067683. PMID 30063702.
  38. ^ Signorovitch, A.Y.; Dellaporta, S.L.; Buss, L.W. (2005). "Molecular signatures for sex in the Placozoa". Proceedings of the National Academy of Sciences of the United States of America. 102 (43): 15518–22. Bibcode:2005PNAS..10215518S. doi:10.1073/pnas.0504031102. PMC 1266089. PMID 16230622.
  39. ^ Charlesworth, D. (2006). "Population genetics: Using recombination to detect sexual reproduction: The contrasting cases of Placozoa and C. elegans". Heredity (Edinb.). 96 (5): 341–342. doi:10.1038/sj.hdy.6800809. PMID 16552431. S2CID 44333533.
  40. ^ Kamm, Kai; Schierwater, Bernd; DeSalle, Rob (2019-01-05). "Innate immunity in the simplest animals – placozoans". BMC Genomics. 20 (1): 5. doi:10.1186/s12864-018-5377-3. ISSN 1471-2164. PMC 6321704. PMID 30611207.
  41. ^ "Deceptively simple: Minute marine animals live in a sophisticated symbiosis with bacteria". Phys.org (Press release). Max Planck Society. 10 June 2019. Retrieved 2021-06-23.
  42. ^ Gruber-Vodicka, Harald; Leisch, Niko; Kleiner, Manuel; Hinzke, Tjorven; Liebeke, Manuel; McFall-Ngai, Margaret; et al. (2019). "Two intracellular and cell type-specific bacterial symbionts in the placozoan Trichoplax H2". Nature Microbiology. 4 (9): 1465–1474. doi:10.1038/s41564-019-0475-9. PMC 6784892. PMID 31182796.
  43. ^ Schierwater, Bernd; Osigus, Hans-Jürgen; Bergmann, Tjard; Blackstone, Neil W.; Hadrys, Heike; Hauslage, Jens; Humbert, Patrick O.; Kamm, Kai; Kvansakul, Marc; Wysocki, Kathrin; DeSalle, Rob (2021). "The enigmatic Placozoa part 2: Exploring evolutionary controversies and promising questions on earth and in space". BioEssays. 43 (10): e2100083. doi:10.1002/bies.202100083. ISSN 0265-9247. PMID 34490659.
  44. ^ Living Mysteries: Meet Earth’s simplest animal
  45. ^ Cuervo-González, Rodrigo (September 2017). "Rhodope placozophagus (Heterobranchia) a new species of turbellarian-like Gastropoda that preys on placozoans". Zoologischer Anzeiger. 270: 43–48. Bibcode:2017ZooAn.270...43C. doi:10.1016/j.jcz.2017.09.005.
  46. ^ Eitel, Michael; Osigus, Hans-Jürgen; Desalle, Rob; Schierwater, Bernd (2013). "Global diversity of the Placozoa". PLOS ONE. 8 (4): e57131. Bibcode:2013PLoSO...857131E. doi:10.1371/journal.pone.0057131. PMC 3614897. PMID 23565136.
  47. ^ Romanova, Daria Y.; Smirnov, Ivan V.; Nikitin, Mikhail A.; Kohn, Andrea B.; Borman, Alisa I.; Malyshev, Alexey Y.; et al. (29 October 2020). "Sodium action potentials in placozoa: Insights into behavioral integration and evolution of nerveless animals". Biochemical and Biophysical Research Communications. 532 (1): 120–126. doi:10.1016/j.bbrc.2020.08.020. PMC 8214824. PMID 32828537.
  48. ^ Romanova, Daria; Nikitin, Mikhail; Shchenkov, Sergey; Moroz, Leonid (2022). "Expanding of life strategies in placozoa: Insights from long-term culturing of Trichoplax and Hoilungia". Frontiers in Cell and Developmental Biology. 10: 823283. doi:10.3389/fcell.2022.823283. PMC 8864292. PMID 35223848.
  49. ^ Romanova, Daria; Varoqueaux, Frederique; Daraspe, Jean; Nikitin, Mikhail; Eitel, Michael; Fasshauer, Dirk; Moroz, Leonid (2021). "Expanding of Life Strategies in Placozoa: Insights From Long-Term Culturing of Trichoplax and Hoilungia". Frontiers in Cell and Developmental Biology. 10: 623–637. doi:10.3389/fcell.2022.823283. PMC 8864292. PMID 35223848.
  50. ^ Sperling, Erik; Vinther, Jakob; Pisani, Davide; Peterson, Kevin (2008). "A placozoan affinity for Dickinsonia and the evolution of Late Precambrian metazoan feeding modes" (PDF). In Cusack, M.; Owen, A.; Clark, N. (eds.). Programme with Abstracts. Palaeontological Association Annual Meeting. Vol. 52. Glasgow, UK. p. 81.
  51. ^ a b c d Srivastava, M.; Begovic, Emina; Chapman, Jarrod; Putnam, Nicholas H.; Hellsten, Uffe; Kawashima, Takeshi; et al. (21 August 2008). "The Trichoplax genome and the nature of placozoans". Nature. 454 (7207): 955–960. Bibcode:2008Natur.454..955S. doi:10.1038/nature07191. PMID 18719581. S2CID 4415492.
  52. ^ Smith CL, Varoqueaux F, Kittelmann M, Azzam RN, Cooper B, Winters CA, et al. (July 2014). "Novel cell types, neurosecretory cells, and body plan of the early-diverging metazoan Trichoplax adhaerens". Current Biology. 24 (14): 1565–1572. Bibcode:2014CBio...24.1565S. doi:10.1016/j.cub.2014.05.046. PMC 4128346. PMID 24954051.
  53. ^ Grasshoff, Manfred; Gudo, Michael (2002). "The origin of metazoa and the main evolutionary lineages of the animal Kingdom: The gallertoid hypothesis in the light of modern research". Senckenbergiana Lethaea. 82 (1). Springer Science and Business Media LLC: 295–314. doi:10.1007/bf03043790. ISSN 0037-2110. S2CID 84989130.
  54. ^ Dellaporta, S.L.; Xu, A.; Sagasser, S.; Jakob, W.; Moreno, M.A.; Buss, L.W.; Schierwater, B.; et al. (6 June 2006). "Mitochondrial genome of Trichoplax adhaerens supports Placozoa as the basal lower metazoan phylum". Proceedings of the National Academy of Sciences of the United States of America. 103 (23): 8751–8756. Bibcode:2006PNAS..103.8751D. doi:10.1073/pnas.0602076103. PMC 1470968. PMID 16731622.
  55. ^ Whelan, Nathan V.; Kocot, Kevin M.; Moroz, Tatiana P.; Mukherjee, Krishanu; Williams, Peter; Paulay, Gustav; et al. (2017-10-09). "Ctenophore relationships and their placement as the sister group to all other animals". Nature Ecology & Evolution. 1 (11): 1737–1746. Bibcode:2017NatEE...1.1737W. doi:10.1038/s41559-017-0331-3. ISSN 2397-334X. PMC 5664179. PMID 28993654.
  56. ^ "Sponges and comb jellies". News and features. www.bristol.ac.uk (Press release). University of Bristol. November 2015. Retrieved 2023-03-11.
  57. ^ Tiny sea creatures reveal the ancient origins of neurons
  58. ^ Najle, Sebastián R.; Grau-Bové, Xavier; Elek, Anamaria; Navarrete, Cristina; Cianferoni, Damiano; Chiva, Cristina; Cañas-Armenteros, Didac; Mallabiabarrena, Arrate; Kamm, Kai; Sabidó, Eduard; Gruber-Vodicka, Harald; Schierwater, Bernd; Serrano, Luis; Sebé-Pedrós, Arnau (2023). "Stepwise emergence of the neuronal gene expression program in early animal evolution". Cell. 186 (21): 4676–4693.e29. doi:10.1016/j.cell.2023.08.027. hdl:10230/58738. PMC 10580291. PMID 37729907.
  59. ^ Pechenik, Jan (2015). "The Poriferans and Placozoans". Biology of the Invertebrates (7 ed.). McGraw-Hill Education. p. 90. ISBN 978-0073524184.
  60. ^ Layden, Michael J. (2018). "Cnidarian Zic genes". In Aruga, Jun (ed.). Zic Family: Evolution, development, and disease. Zic family in animal evolution and development. Advances in Experimental Medicine and Biology. Vol. 1046 (1st ed.). Singapore: Springer Nature Singapore (published 14 February 2018). pp. 27–39. doi:10.1007/978-981-10-7311-3_2. ISBN 978-981-10-7310-6. ISSN 0065-2598. PMID 29442315.
  61. ^ Wallberg, Andreas; Thollesson, Mikael; Farris, James S.; Jondelius, Ulf (2004-12-01). "The phylogenetic position of the comb jellies (Ctenophora) and the importance of taxonomic sampling". Cladistics. 20 (6): 558–578. doi:10.1111/j.1096-0031.2004.00041.x. ISSN 1096-0031. PMID 34892961. S2CID 86185156.
  62. ^ Laumer, C.E.; Fernández, R.; Lemer, S.; Combosch, D.; Kocot, K.M.; Riesgo, A.; et al. (2019). "Revisiting metazoan phylogeny with genomic sampling of all phyla". Proc. Biol. Sci. 286 (1906): 20190831. doi:10.1098/rspb.2019.0831. PMC 6650721. PMID 31288696.
  63. ^ Aleshin, V.V.; Petrov, N.B. (2002). "Molecular evidence of regression in evolution of metazoa". Zh. Obshch. Biol. 63 (3): 195–208. PMID 12070939.
  64. ^ Laumer, Christopher E.; Gruber-Vodicka, Harald; Hadfield, Michael G.; Pearse, Vicki B.; Riesgo, Ana; Marioni, John C.; Giribet, Gonzalo (30 October 2018). "Support for a clade of Placozoa and Cnidaria in genes with minimal compositional bias". eLife. 7. doi:10.7554/elife.36278. ISSN 2050-084X. PMC 6277202. PMID 30373720.
  65. ^ Syed, Tareq; Schierwater, Bernd (June 2002). "The evolution of the placozoa: A new morphological model". Senckenbergiana Lethaea. 82 (1): 315–324. doi:10.1007/bf03043791. ISSN 0037-2110. S2CID 16870420.
  66. ^ Hejnol, Andreas; Martindale, Mark Q. (27 April 2008). "Acoel development supports a simple planula-like urbilaterian". Philosophical Transactions of the Royal Society B: Biological Sciences. 363 (1496): 1493–1501. doi:10.1098/rstb.2007.2239. ISSN 0962-8436. PMC 2614228. PMID 18192185.
  67. ^ Alzugaray, María Eugenia; Bruno, María Cecilia; Villalobos Sambucaro, María José; Ronderos, Jorge Rafael (2019). "The evolutionary history of the orexin / allatotropin GPCR family: From Placozoa and Cnidaria to Vertebrata". Scientific Reports. 9 (1): 10217. Bibcode:2019NatSR...910217A. bioRxiv 10.1101/403709. doi:10.1038/s41598-019-46712-9. PMC 6629687. PMID 31308431. S2CID 256990037.
  68. ^ da Silva, Fernanda Britto; Muschner, Valéria C.; Bonatto, Sandro L. (2007). "Phylogenetic position of Placozoa based on large subunit (LSU) and small subunit (SSU) rRNA genes". Genetics and Molecular Biology. 30 (1): 127–132. doi:10.1590/S1415-47572007000100022. ISSN 1415-4757.
  69. ^ Adl, Sina M.; Bass, David; Lane, Christopher E.; Lukeš, Julius; Schoch, Conrad L.; Smirnov, Alexey; et al. (26 September 2018). "Revisions to the classification, nomenclature, and diversity of eukaryotes". Journal of Eukaryotic Microbiology. 66 (1): 4–119. doi:10.1111/jeu.12691. ISSN 1066-5234. PMC 6492006. PMID 30257078.
  70. ^ Giribet, Gonzalo; Edgecombe, Gregory D. (3 March 2020). The Invertebrate Tree of Life. Princeton University Press. ISBN 978-0-691-19706-7.
  71. ^ duBuc, Timothy Q.; Ryan, Joseph; Martindale, Mark Q. (6 February 2019). ""Dorsal-ventral" genes are part of an ancient axial patterning system: Evidence from Trichoplax adhaerens (Placozoa)". Molecular Biology and Evolution. 36 (5): 966–973. doi:10.1093/molbev/msz025. ISSN 0737-4038. PMC 6501881. PMID 30726986.
  72. ^ Schuchert, Peter (1 March 1993). "Trichoplax adhaerens (phylum Placozoa) has cells that react with antibodies against the neuropeptide RFamide". Acta Zoologica. 74 (2): 115–117. doi:10.1111/j.1463-6395.1993.tb01227.x. ISSN 1463-6395.
[edit]
Wikispecies has information related to Placozoa.
Wikimedia Commons has media related to Placozoa.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Placozoa&oldid=1260449761"