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Zooxanthellae are protists that can live as endosymbionts in a number of living things. The zooxanthellae are mostly dinoflagellates , but chrysomonads , cryptomonads or diatoms also occur. The hosts are rhizaria (chamberlings alias foraminifera and radiolucent animals alias radiolaria ), stony corals (Scleractinia), many octocorallia , other flower animals (anthozoa), fire corals ( Millepora ), giant clams (Tridacnidae), but also some types of jellyfish . Also nudibranchs (Nudibranchia, z. B. Pteraeolidia ianthina ) and sponges sometimes have zooxanthellae. All corals that are involved in the construction of tropical coral reefs have zooxanthellae as endosymbionts.

Cross-section through the mantle tissue of a giant clam that carries symbiotic protozoa (zooxanthellae).

The zooxanthellae live in the host's body and supply it with sugar , starch and other organic products. Both the host and the protists benefit from the symbiosis , so it is a matter of mutualism. In the foraminifera , the symbiosis is optional, that is, both creatures in principle thrive without each other. The reef-forming hard corals of tropical coral reefs, on the other hand, die when they expel their zooxanthellae under stress, a phenomenon known as coral bleaching .

Schematic drawing of Lithocircus annularis , a Radiolarie (Strahlentierchen) from the class Ploycystinea , Order Nasellaria with Zooxanthellen ( z ), pseudopodia ( psd ), cytoskeleton ( skel ) and the nucleus ( Nu )

If it is not the protist cells as a whole but only the chloroplasts that are preserved, this is called kleptoplasty .

Individual evidence

  1. The radiolarians are probably polyphyletic and are composed of the taxa Polycystinea , Acantharia and Sticholonchia , which, like the Foraminifera, all belong to the Rhizaria; see Radiolaria .
  2. ^ Klaus Hausmann, Norbert Hülsmann, Renate Radek: Protistology . 3. Edition. Schweizerbart, 2003, ISBN 3-510-65208-8 , pp. 341 .
  3. Bill Rudman: Zooxanthellae in nudibranchs on seaslugforum.net.
  4. S. Mariani, M.-J. Uriz, X. Turon: Larval Bloom of the oviparous sponge Cliona viridis : Coupling of larval abundance and adult distribution . In: Marine Biology (2000) 137: pp. 783-790
  5. ^ Peter Sitte , Elmar Weiler , Joachim W. Kadereit , Andreas Bresinsky , Christian Körner : Textbook of botany for universities . Founded by Eduard Strasburger . 35th edition. Spektrum Akademischer Verlag, Heidelberg 2002, ISBN 3-8274-1010-X , p. 704 .
  6. Klaus Nuglisch: Foraminiferen - marine Mikroorganismen , Wittenberg, A. Ziemsen Verlag 1985, ISBN 3740301155 , p. 25.
  7. Helmut Schuhmacher, Karen Loch, Wolfgang Loch, Wolf R. See: The bleaching of the corals . In: Biology in our time 3/2005: pp. 186–191, doi: 10.1002 / biuz.200410281
  8. Lithocircus on: Taxonomicon

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