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

Rhizaria representa un grupo diverso de protistas que poseen seudópodos filiformes. Hay tres subgrupos principales: Chlorarachniophyta, Foraminíferos y Radiolaria. Las cloracniofitas son protistas fototróficos que se encuentran tanto en ambientes de agua dulce como marinos. Tienen cloroplastos con cuatro membranas debido a los endosimbiontes de algas que se adquirieron durante la endosimbiosis secundaria. Los foraminíferos son estrictamente protistas marinos que construyen estructuras en forma de concha llamadas test, compuestas de carbonato de calcio y material orgánico. La mayoría de los foraminíferos se extienden hacia afuera de sus pruebas para alimentarse de materia orgánica en descomposición, bacterias u otros pequeños protistas en el fondo del océano. Algunos foraminíferos son planctónicos y albergan algas endosimbióticas para obtener nutrientes. Los radiolarios son quimioorganótrofos planctónicos marinos. Poseen pruebas compuestas de sílice. Los radiolarios habitan en los 100 m superiores del océano, donde permanecen suspendidos por gotas de lípidos, grandes vacuolas citoplasmáticas y seudópodos en forma de aguja. Se alimentan de bacterias y materia orgánica. Por el contrario, algunas otras especies establecen relaciones simbióticas, pero no endosimbióticas, con las algas.

diversidad de protistas-iii

Diversity of Protists III

Rhizaria constituye un grupo diverso de protistas unicelulares caracterizados por sus extensiones citoplasm&#225;ticas filamentosas denominadas seud&#243;podos. Estas estructuras facilitan tanto la locomoci&#243;n como la alimentaci&#243;n, otorgando a los Rhizaria una apariencia ameboide. Su morfolog&#237;a ameboide gener&#243; anteriormente confusi&#243;n taxon&#243;mica, pero la filogenia molecular ha esclarecido su posici&#243;n evolutiva y ha puesto de relieve el uso compartido de seud&#243;podos a pesar de pertenecer a linajes divergentes.
Este clado incluye linajes diversos como Chlorarachniophyta, Radiolaria y Foraminifera, todos los cuales se han adaptado a nichos ecol&#243;gicos espec&#237;ficos y presentan una variedad de estrategias metab&#243;licas.
Chlorarachniophyta
Los Chlorarachniophyta son protistas fototr&#243;ficos unicelulares presentes en ambientes tanto marinos como de agua dulce. Constituyen un ejemplo de endosimbiosis secundaria, en la cual un hospedador eucariota no fotosint&#233;tico fagocit&#243; un alga eucariota fotosint&#233;tica. A diferencia de los plastidios primarios que suelen presentar dos membranas, los cloroplastos de los chlorarachniophytes est&#225;n rodeados por cuatro membranas y conservan un nucleomorfo&#8212;un n&#250;cleo vestigial procedente del alga fagocitada. Este nucleomorfo representa un estado intermedio poco com&#250;n en la integraci&#243;n de plastidios, conservando evidencia gen&#243;mica y estructural del evento endosimbi&#243;tico.
La arquitectura gen&#233;tica de los chlorarachniophytes es inusualmente compleja. Se reconocen al menos cinco genomas: (1) el genoma nuclear del hospedador, (2) el genoma mitocondrial del hospedador, (3) el genoma del nucleomorfo, (4) el genoma mitocondrial del alga y (5) el genoma plast&#237;dico. A lo largo de la evoluci&#243;n, muchos genes del endosimbionte se han transferido al n&#250;cleo del hospedador, lo que ha conllevado una reducci&#243;n gen&#243;mica en el nucleomorfo y en el cloroplasto. Esta integraci&#243;n gen&#243;mica refleja una racionalizaci&#243;n evolutiva, en la cual se eliminan o reasignan funciones redundantes.
Foraminifera
Los foramin&#237;feros son protistas marinos ameboides que construyen testas elaboradas, frecuentemente compuestas de carbonato c&#225;lcico. Estas testas no forman parte de la c&#233;lula viva, pero proporcionan protecci&#243;n estructural y sustentan la alimentaci&#243;n mediante seud&#243;podos. Los foramin&#237;feros bent&#243;nicos habitan el fondo oce&#225;nico, donde se alimentan de materia org&#225;nica particulada y establecen simbiosis de intercambio de nutrientes con algas. Las especies planct&#243;nicas albergan endosimbiontes fototr&#243;ficos y ocupan las capas superficiales del oc&#233;ano donde la luz solar es accesible.
El potencial de fosilizaci&#243;n de las testas foramin&#237;feras las convierte en herramientas indispensables en biostratigraf&#237;a y geolog&#237;a del petr&#243;leo. Su distribuci&#243;n en los estratos geol&#243;gicos permite inferir la edad relativa de las capas sedimentarias y evaluar el potencial de presencia de yacimientos petrol&#237;feros.
Radiolaria
Los radiolarios son protistas marinos planct&#243;nicos que habitan principalmente aguas superficiales. Sus esqueletos sim&#233;tricos de s&#237;lice son altamente ornamentados y persisten tras la muerte, contribuyendo a la formaci&#243;n de lodos sil&#237;ceos en el fondo marino. Los radiolarios se alimentan de detritos org&#225;nicos y bacterias, y ocasionalmente forman relaciones simbi&#243;ticas con algas. A diferencia de los foramin&#237;feros, los radiolarios no participan en procesos de endosimbiosis. Su flotabilidad se mantiene mediante inclusiones lip&#237;dicas, vacuolas y seud&#243;podos r&#237;gidos que contrarrestan el hundimiento por gravedad.

Diversidad de Protistas-III

Rhizaria constituye un grupo diverso de protistas unicelulares caracterizados por sus extensiones citoplasm&#225;ticas filamentosas denominadas ...

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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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