Radiation animals

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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.

Strahlentierchen or Radiolarien (Radiolaria, lat . Radiolus "small beam") are a group of single-celled organisms with an endoskeleton from Opal ( silica , SiO 2 ), belonging to the eukaryotes belongs.

The radiolarians have radially protruding cytoplasmic appendages ( axopodia ), which are supported on the inside with thin, rigid spikes made of silicon dioxide and bundles of microtubules made of protein . The silicon dioxide supports radiate out from an endoskeleton which is also made of silicon dioxide and consists of a spherical, perforated capsule or several concentrically arranged capsules of this type. Radiolarians therefore have a " pebbly " skeleton, which, however, contains not only silicon dioxide but also organic components. Species of the Acantharea group are an exception, they form the spines from strontium sulfate .

Table with radiolarians from Haeckel's "Art Forms of Nature"

The drawings of radiolarian skeletons that Ernst Haeckel made and published in the monograph "Die Radiolarien" in 1862 became very well known .

features

The size of the spherical or cap-shaped skeletons is usually between 50 and 500 μm . The axopodia are used to float in the water and to take in food. Radiolarians are heterotrophic and take up dissolved nutrients from the water or particulate nutrients that get caught in the axopodia. There are forms that form colonies held together with a jelly . The mitochondria are located inside the skeletal capsule, while the cytoplasm outside the capsule contains vacuoles ( fluid-filled space delimited by a cytoplasmic membrane ). In the outer cytoplasm, unicellular algae are also sometimes absorbed as phototrophic symbionts .

Ecology and tribal history

Radiolarians only occur as plankton in the sea, especially in near-surface areas of warmer parts of the Pacific and Indies (rarely in the Atlantic).

Clear first fossil records of the group come from the Central Cambrian of Australia (from the 507 to 505 million year old Inca Formation of the Georgina Basin in Queensland ), but their origin is probably in the Neoproterozoic .

In the course of the Paleozoic , the predominant radiolarian order (or subordination) was the ectinaria . With the beginning of the Triassic , they were gradually displaced by the Spumellaria and then almost died out at the Triassic-Jura border . From the Pennsylvania onwards , in addition to the Ectinaria, the Albaillellaria also gained a very important position among the radiolarians, which they were to maintain until the beginning of the Upper Triassic - the time of their extinction. The spumellaria also suffered severely in this mass extinction and lost around two thirds of their taxa. The Nassellaria benefited from this as they experienced an enormous upswing in their biodiversity and then formed the predominant radiolarian order up to the Cretaceous-Tertiary border . However, the number of species of the Nassellaria was reduced by over two thirds at the K / T border and thus enabled the final rise of the Spumellaria, which currently represent the most species-rich radiolarian order.

Geological importance

Small spherical radiolarians (with large foraminifera ) from an approx. 12,000 year old sediment sample from the Antarctic continental slope . Average diameter of the radiolarians 0.5 mm

In addition to sponges and diatoms, radiolarians are rock-forming organisms with an opal skeleton (Opal A). If their deposits are enriched en masse, they form pebbly biogenic sediments . Radiolarians are found in very large quantities in the oceans and extract silicon dioxide from the water to build their skeletons. After they die, they sink, whereby the organic components are decomposed and only the skeletal material remains. At the sea bottom , a reddish-brown, greenish black or gray forms Radiolarienschlamm from Skelettopal (water-containing amorphous SiO 2 ). Radiolarian sludge covers about 2.6% of the sea floor (main area of ​​distribution in the equatorial western Pacific) and consists of 30-80% of radiolarian skeleton material, on average they contain about 55% pebbly components, the remaining sediment portion consists predominantly of lime, which for the most part consists of the shells of Foraminifera originates.

Under the pressure of the overlying layers, the sediment solidifies and the organically created, unstable opal is gradually transformed into opal CT and finally into stable micro-quartz as the diagenesis (rock formation) progresses . This results radiolarites even Hornstein called. Black chert is often referred to as lydite or, somewhat misleadingly, silica slate .

Systematics

Before the era of phylogenomics , the radiolaria appeared to be a well-established group due to the features of the skeleton. Since pedigrees based on the comparison of homologous DNA sequences can be set up as a new feature, the traditional group has been increasingly questioned. First it turned out in 2004 that the Phaeodarea must be more closely related to the Cercozoa than to the other Radiolaria. Thomas Cavalier-Smith drew the consequence from this to spin off the Phaeodarea; the remaining taxon from the remaining two groups (in the classical system in the rank of classes), the Acantharea and Polycystinea, he summarized as a new taxon under the name Radiozoa. According to this theory, the Radiozoa together with the Foraminifera (chamberlings) formed the Retaria department .

Later investigations have shown that the Radiozoa in the sense of Cavalier-Smith may not be a monophyletic taxon. It turned out to be a possibility that the (even monophyletic) foraminifera (with calcareous skeletons) do not form the sister group of the Acantharea and the Polycystinea together, but are nested in them. Although this result had been known for some time, it was still suspected that it could be a data artifact due to different evolution speeds (so-called long-branch attraction ). The grouping was also shown in analyzes using numerous genes. The foraminifera are possibly the sister group of the Acantharea. The two other classes of the former radiolaria would no longer form a common taxon, but a paraphyletic union.

This result was also called into question by other investigators. Numerous newer systems, such as WoRMS or the Handbook of the Protists, therefore adhere to a monophyletic group that corresponds to the Radiozoa.

All more modern analyzes agree at least that the Rhizaria , the Retaria and the Foraminifera are monophyletic taxa. Whether a Phylum Radiozoa exists or how the groups belonging to it can be arranged alternatively has been controversial until recently, all published phylogenies are unstable and contradicting one another.

The system (here according to Cavalier-Smith 2018) would look like this as a possibility:

  • Infraphylum Radiozoa Cavalier-Smith, 1987
    • Class Polycystinea Ehrenberg, 1838
      • Order Collodarida Haeckel, 1881 (alternatively written Collodaria)
      • Order Nassellaria Ehrenberg, 1875
      • Order Spumellaria Ehrenberg, 1875
    • Class Acantharia Haeckel, 1881 stat. n. Cavalier-Smith, 1993 (also written Acantharea) skeleton consists of strontium sulfate .
      • Order Arthracanthida Schewiakoff, 1926 (here including the Symphyacanthida Schewiakoff, 1926)
      • Order Chaunacanthida Schewiakoff, 1926
      • Order Holacanthida Schewiakoff, 1926
      • Order Acanthoplegmida Rechetniak, 1981
  •  Infraphylum Sticholonchia Cavalier-Smith 2018 (with the order Taxopodida and the only species Sticholonche zanclea Hertwig, 1877, formerly part of the sun animals )

The structure of the Polycystinea corresponds to that in the Handbook of the Protists 2016. Some authors even maintain the old name Radiolaria for the (controversial) clade from Polycystinea and Acantharia.

In oceanology and marine ecology, a group of radiolarians is often maintained as a form taxon and an ecological group. This grouping is also still common for fossil taxa, which can only be classified according to skeletal features.

Research history

Radiolariums were described for the first time by Franz Julius Ferdinand Meyen in 1834 (including the genus Sphaerozoum ), and he provided three images at the same time. From 1838 Christian Gottfried Ehrenberg carried out important work on radiolarians; by 1875 he detailed several hundred living or fossil taxa of the Cenozoic era . The term radiolaria was established in 1858 by Johannes Müller ; he was also the first to recognize radiolarians as single-cell organisms. In a synthesis in 1879, based on the capsule morphology, he created the first subdivision into different groups. Ernst Haeckel followed him with his monumental work, which was published in 1887; on 1,800 pages and 140 illustration panels he described 785 new species. He also created a new, geometrically inspired classification by shaping the pebble skeleton, which was used until the 1970s.

With his cytological study Histology of Radiolarians from 1876 Richard von Hertwig published a groundbreaking study of the tissue structure of radiolarians.

Between the beginning of the First World War and the early 1950s, radiolarian research had stalled, partly due to the adherence to Haeckel's classification system. It was not until 1952 that new scientific advances were made with William Riedel . With the help of profiles, Riedel was able to make it clear that the radiolarians, like other protists, had evolved during the Cenozoic and were therefore also valuable stratigraphic indicators. Riedel's work was funded significantly by the deep-sea drilling of the DSDP and ODP . In 1962, Maria Petrushevskaya finally established a natural classification of radiolarians that deviated from Haeckel and was based on the inner skeleton and its evolution.

In the 1970s, the first radiolarion zones were identified by biostratigraphy , initially for the Chalk , and later also for the Jura and Triassic .

Whetstone limestone from the Ammer Mountains with radiolarian remains (thin section)

Commercial importance

In the Ammer Mountains and especially near Unterammergau , Jurassic limestones occur in the Alps , which contain up to 12.5% ​​silicon dioxide in the form of radiolar skeletons. These stones were mined as raw material for local whetstone grinders until the middle of the 20th century . The abrasive effect of the whetstones made from them results from the even distribution of the hard radiolar skeletons in the soft limestone matrix.

Individual evidence

  1. ^ Erwin J. Hentschel, Günther H. Wagner: Zoological dictionary . 6th edition. Gustav Fischer Verlag Jena, Jena 1996, p. 507 .
  2. ^ Rieger, Reinhard; Westheide, Wilfried: Special Zoology Part 1: Protozoa and Invertebrates Spectrum; Stuttgart 2006; ISBN 3-8274-1575-6
  3. ↑ a b c d Peter Rothe: Rocks. Creation - destruction - transformation . 1st edition. Scientific Book Society, Darmstadt 1994, p. 94 .
  4. ↑ Won, M.-Z. & Below, R .: Cambrian Radiolaria from the Georgina Basin, Queensland, Australia . In: Micropaleontology . tape 45 (4) , 1999, p. 325-363 .
  5. ^ Kozur, H. & Mostler, H .: Ectinaria subordo nov., A new radiolarian suborder . In: Geol. Paleontol. Mitt. Innsbruck . tape 11/12 , 1982, pp. 399-414 .
  6. ↑ Peter Rothe: Rocks. Creation - destruction - transformation . 1st edition. Scientific Book Society, Darmstadt 1994, p. 93 .
  7. ^ Thomas Cavalier-Smith (2003): Protist phylogeny and the high-level classification of Protozoa. European Journal of Protistology 39: 338-348. doi: 10.1078 / 0932-4739-00002
  8. ↑ Roberto Sierra, Mikhail V. Matz, Galina Aglyamova, Loïc Pillet, Johan Decelle, Fabrice Not, Colomban de Vargas, Jan Pawlowski (2013): Deep relationships of Rhizaria revealed by phylogenomics: A farewell to Haeckel's Radiolaria. Molecular Phylogenetics and Evolution 67: 53-59. doi: 10.1016 / j.ympev.2012.12.011
  9. ↑ Roberto Sierra, Silvia J. Canas-Duarte, Fabien Burki, Arne Schwelm, Johan Fogelqvist, Christina Dixelius, Laura N. Gonzalez-Garcıa, Gillian H. Gile, Claudio H. Slamovits, Christophe Klopp, Silvia Restrepo, Isabelle Arzul, Jan Pawlowski (2016): Evolutionary Origins of Rhizarian Parasites. Molecular Biology and Evolution 33 (4): 980-983 doi: 10.1093 / molbev / msv340
  10. ↑ Thomas Cavalier-Smith, Ema E. Chao, Rhodri Lewis (2018): Multigene phylogeny and cell evolution of chromist infrakingdom Rhizaria: contrasting cell organization of sister phyla Cercozoa and Retaria. Protoplasm 255 (5): 1517-1574. doi: 10.1007 / s00709-018-1241-1
  11. ↑ phylum Radiozoa . World Register of Marine Species, accessed November 26, 2018
  12. ↑ Demetrio Boltovskoy, O. Roger Anderson, Nancy M. Correa: Radiolaria and Phaeodaria. In: JM Archibald, AGB Simpson, CH Slamovits (editors): Handbook of the Protists. 2nd edition 2016. Springer Verlag, Berlin, Heidelberg etc. doi: 10.1007 / 978-3-319-32669-6_19-1
  13. ↑ Jean-David Grattepanche, Laura M. Walker, Brittany M. Ott, Daniela L. Paim Pinto, Charles F. Delwiche, Christopher E. Lane, Laura A. Katz (2018): Microbial Diversity in the Eukaryotic SAR Clade: Illuminating the Darkness Between Morphology and Molecular Data. BioEssays 40 (4) (12 pages) doi: 10.1002 / bies.201700198
  14. ^ Stefan Glaser, Ulrich Lagally, Georg Loth, Hubert Schmid, Klaus Schwerd: Geotope in Upper Bavaria . In: Bavarian State Office for the Environment (Ed.): Earth science contributions to nature conservation . tape 6 . Augsburg 2008, ISBN 978-3-940009-94-4 , pp. 128-129 .

literature

  • Johannes Müller : About the Thalassicollen, Polycystinen and Acanthometren of the Mediterranean Sea . Treatises of the Royal Academy of Sciences in Berlin, 1858 pp. 1–62.
  • David Rust : Contributions to the knowledge of fossil radiolarians from Jura rocks, by Dr. Armor, ... , T. Fischer, 1885
  • David Rust: Contributions to the knowledge of fossil radiolarians from chalk rocks, by Dr. Armor, ... E. Koch, 1887
  • David Rust: Contributions to the knowledge of fossil radiolarians from rocks of the Triassic and the Palaeozoic layers, by Dr. Armor, ... , E. Koch, 1891
  • David Rust: New contributions to the knowledge of fossil radiolarians from rocks of the Jura and the Chalk, by Dr. Armor, ... , E. Naegele, 1898

Web links

Commons : Radiolarians  - Collection of images, videos and audio files