Name: rhizaria: pseudopods, tests, and skeletons
Uploaded: 2025-06-12T06:30:33.000Z
Duration: 1 min 27 s
Channel: JoVE

Rhizarien stellen eine vielfältige Gruppe von Protisten dar, die fadenförmige Pseudopodien besitzen. Es gibt drei Hauptuntergruppen – Chlorarachniophyta, Foraminifera und Radiolaria. Chlorarachniophyta sind phototrophe Protisten, die sowohl in Süßwasser- als auch in Meeresumgebungen vorkommen. Sie haben Chloroplasten mit vier Membranen, die auf Algen-Endosymbionten zurückzuführen sind, die während der sekundären Endosymbiose erworben wurden. Foraminiferen sind streng marine Protisten, die schalenartige Strukturen, sogenannte Tests, aus Kalziumkarbonat und organischem Material bilden. Die meisten Foraminiferen strecken sich von ihren Tests nach außen, um sich von zerfallendem organischem Material, Bakterien oder anderen kleinen Protisten auf dem Meeresboden zu ernähren. Einige Foraminiferen sind planktonisch und beherbergen endosymbiotische Algen, um Nährstoffe zu erhalten. Radiolarien sind chemoorganotrophe Pflanzen der Meeresplanktonik. Sie verfügen über Tests, die aus Kieselsäure bestehen. Radiolarien bewohnen die oberen 100 m des Ozeans, wo sie von Lipidtröpfchen, großen zytoplasmatischen Vakuolen und nadelförmigen Pseudopodien in der Schwebe gehalten werden. Sie ernähren sich von Bakterien und organischem Material. Im Gegensatz dazu gehen einige andere Arten symbiotische, aber nicht endosymbiotische Beziehungen mit Algen ein.

diversität der protisten-iii

Diversity of Protists III

Rhizaria sind eine vielf&#228;ltige Gruppe einzelliger Protisten, die durch ihre fadenf&#246;rmigen zytoplasmatischen Ausst&#252;lpungen, sogenannte Pseudopodien, charakterisiert sind. Diese Strukturen unterst&#252;tzen sowohl die Fortbewegung als auch die Nahrungsaufnahme und verleihen den Rhizaria ein am&#246;boides Erscheinungsbild. Aufgrund ihrer am&#246;boiden Morphologie kam es fr&#252;her zu taxonomischen Missverst&#228;ndnissen, doch molekulare Phylogenetik hat ihre evolution&#228;re Einordnung gekl&#228;rt und die gemeinsame Nutzung von Pseudopodien trotz unterschiedlicher Abstammungslinien hervorgehoben.
Diese Klade umfasst vielf&#228;ltige Linien wie Chlorarachniophyta, Radiolaria und Foraminifera, die sich an unterschiedliche &#246;kologische Nischen angepasst haben und eine Vielzahl metabolischer Strategien aufweisen.
Chlorarachniophyta
Chlorarachniophyta sind einzellige phototrophe Protisten, die in marinen und S&#252;&#223;wasserhabitaten vorkommen. Sie repr&#228;sentieren ein Beispiel f&#252;r sekund&#228;re Endosymbiose, bei der ein nicht-photosynthetischer eukaryotischer Wirt eine photosynthetisch aktive Alge aufnahm. Im Gegensatz zu prim&#228;ren Plastiden, die typischerweise von zwei Membranen umgeben sind, besitzen die Chloroplasten der Chlorarachniophyten vier Membranen und enthalten ein Nukleomorph &#8211; einen rudiment&#228;ren Zellkern der aufgenommenen Alge. Dieses Nukleomorph stellt ein seltenes intermedi&#228;res Stadium bei der Integration von Plastiden dar und bewahrt genomische sowie strukturelle Belege des endosymbiotischen Ereignisses.
Die genetische Architektur der Chlorarachniophyten ist au&#223;ergew&#246;hnlich komplex. Es sind mindestens f&#252;nf Genome vorhanden: (1) das nukle&#228;re Genom des Wirts, (2) das mitochondriale Genom des Wirts, (3) das Genom des Nukleomorphs, (4) das mitochondriale Genom der Alge und (5) das Plastidengenom. Im Verlauf der Evolution wurden viele Gene des Endosymbionten in den Zellkern des Wirts &#252;bertragen, was zu einer genomischen Reduktion innerhalb des Nukleomorphs und des Chloroplasten f&#252;hrte. Diese genomische Integration spiegelt eine evolution&#228;re Optimierung wider, bei der redundante Funktionen eliminiert oder umorganisiert wurden.
Foraminifera
Foraminiferen sind marine am&#246;boide Protisten, die kunstvoll gestaltete Geh&#228;use bilden, die h&#228;ufig aus Calciumcarbonat bestehen. Diese Geh&#228;use sind kein lebender Zellbestandteil, bieten jedoch strukturellen Schutz und unterst&#252;tzen die Nahrungsaufnahme &#252;ber Pseudopodien. Benthische Foraminiferen leben auf dem Meeresboden, ern&#228;hren sich von organischem Partikelmaterial und gehen n&#228;hrstoffbezogene Symbiosen mit Algen ein. Planktische Arten beherbergen phototrophe Endosymbionten und leben in den oberen Wasserschichten der Ozeane, wo Licht zug&#228;nglich ist.
Die Fossilisierungspotenz der foraminiferen Geh&#228;use macht sie in der Biostratigraphie und Erd&#246;lgeologie unentbehrlich. Ihre Verbreitung in geologischen Schichten erm&#246;glicht R&#252;ckschl&#252;sse auf das relative Alter von Sedimentlagen und die Bewertung m&#246;glicher Erd&#246;lvorkommen.
Radiolaria
Radiolarien sind haupts&#228;chlich planktonische marine Protisten, die in den Oberfl&#228;chengew&#228;ssern leben. Ihre symmetrischen, auf Silikat basierenden Skelette sind hochornamentiert und bleiben nach dem Tod bestehen, wodurch sie zur Bildung von Kieselgur auf dem Meeresboden beitragen. Radiolarien ern&#228;hren sich von organischem Detritus und Bakterien und bilden gelegentlich symbiotische Beziehungen mit Algen. Im Gegensatz zu Foraminiferen betreiben Radiolarien keine Endosymbiose. Ihre Auftriebskraft wird durch Lipideinschl&#252;sse, Vakuolen und starre Pseudopodien aufrechterhalten, die das Absinken unter dem Einfluss der Schwerkraft verhindern.

Diversität der Protisten-III

Rhizaria sind eine vielf&#228;ltige Gruppe einzelliger Protisten, die durch ihre fadenf&#246;rmigen zytoplasmatischen Ausst&#252;lpungen, sogenannte ...

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rhizaria: pseudopods, tests, and skeletons

Rhizaria are unicellular protists with threadlike pseudopodia, which are thin cytoplasmic extensions used for movement and feeding. Their amoeboid shape once caused taxonomic confusion, but molecular phylogenetics has since shown where they fit on the evolutionary tree. This group includes Chlorarachniophyta, Radiolaria, and Foraminifera, and each lineage has adapted to a different ecological niche and metabolic strategy.

Chlorarachniophyta are unicellular phototrophic protists found in marine and freshwater environments. They are a clear example of secondary endosymbiosis, where a non-photosynthetic eukaryotic host engulfed a photosynthetic algal eukaryote. Their chloroplasts have four membranes, unlike the two membranes seen in primary plastids, and they also keep a nucleomorph, which is the vestigial nucleus of the engulfed alga.

Chlorarachniophytes also have unusually complex genetics. At least five genomes are present: the host nuclear genome, the host mitochondrial genome, the nucleomorph genome, the algal mitochondrial genome, and the plastid genome. Over time, many genes moved from the endosymbiont to the host nucleus. This left the nucleomorph and chloroplast reduced and shows how cells can streamline after endosymbiosis.

Foraminifera are marine amoeboid protists that build tests, which are protective shells often made of calcium carbonate. The test is not part of the living cell, but it supports the cell and helps with feeding through pseudopodia. Benthic foraminiferans live on the ocean floor and feed on particulate organic matter, and some also form nutrient-exchange symbioses with algae.

Other foraminiferans are planktonic and live in the upper ocean where sunlight is available. These species can host phototrophic endosymbionts. Their tests fossilize well, which makes foraminifera useful in biostratigraphy and petroleum geology. Scientists use their fossils to compare the relative age of sediment layers and to help judge where oil deposits may be found.

Radiolaria are mostly planktonic marine protists found in surface waters. They have ornate, symmetrical skeletons made of silica, and these structures remain after death to form siliceous ooze on the seafloor. Radiolarians feed on organic detritus and bacteria, and some live with algae in symbiosis. Unlike foraminifera, they do not use endosymbiosis. Their buoyancy comes from lipid inclusions, vacuoles, and stiff pseudopodia that help keep them from sinking.

Rhizaria: Pseudopods, Tests, and Skeletons

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diversity of protists iii

Rhizaria are unicellular protists with threadlike pseudopodia, which are thin cytoplasmic extensions used for movement and feeding. Their amoeboid shape once caused taxonomic confusion, but molecular phylogenetics has since shown where they fit on the evolutionary tree. This group includes Chlorarachniophyta, Radiolaria, and Foraminifera, and each lineage has adapted to a different ecological niche and metabolic strategy. Chlorarachniophyta are unicellular phototrophic protists found in marine...

diversity of protists iv

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key terms and concepts

Explore Rhizaria in high school biology, including pseudopodia, chlorarachniophytes, foraminifera, and radiolarians with their unique structures and roles.

Rhizaria: Pseudopods, Tests, and Skeletons | JoVE K12

JoVE Core Microbiology provides an engaging introduction to the microbial world and its influence on health, industry, and the environment. This comprehensive collection covers key concepts such as microbial structure, metabolism, genetics, and ecology. It introduces essential laboratory techniques and microscopy methods through visually engaging animations. Corresponding scientist-in-action videos bridge classroom concepts with real-world research and applications.

microbiology

Rhizaria: Pseudopods, Tests, and Skeletons

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