Name: rhizaria: pseudopods, tests, and skeletons
Uploaded: 2025-06-12T06:30:33.000Z
Duration: 1 min 27 s
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Rhizaria representa um grupo diversificado de protistas que possuem pseudópodes filiformes. Existem três subgrupos principais - Chlorarachniophyta, Foraminíferos e Radiolaria. Chlorarachniophyta são protistas fototróficos encontrados em ambientes de água doce e marinhos. Eles têm cloroplastos com quatro membranas devido a endossimbiontes de algas que foram adquiridos durante a endossimbiose secundária. Os foraminíferos são protistas estritamente marinhos que constroem estruturas semelhantes a conchas chamadas testes, compostas de carbonato de cálcio e material orgânico. A maioria dos foraminíferos se estende para fora de seus testes para se alimentar de matéria orgânica em decomposição, bactérias ou outros pequenos protistas no fundo do oceano. Alguns foraminíferos são planctônicos e hospedam algas endossimbióticas em busca de nutrientes. Radiolários são quimioorganotróficos planctônicos marinhos. Eles possuem testes compostos de sílica. Os radiolários habitam os 100 m superiores do oceano, onde permanecem suspensos por gotículas lipídicas, grandes vacúolos citoplasmáticos e pseudópodes em forma de agulha. Eles se alimentam de bactérias e matéria orgânica. Em contraste, algumas outras espécies estabelecem relações simbióticas, mas não endossimbióticas, com as algas.

diversidade dos protistas-iii

Diversity of Protists III

Rhizaria s&#227;o um grupo diverso de protistas unicelulares caracterizados por suas extens&#245;es citoplasm&#225;ticas filamentosas conhecidas como pseud&#243;podes. Essas estruturas auxiliam tanto na locomo&#231;&#227;o quanto na alimenta&#231;&#227;o, conferindo aos Rhizaria uma apar&#234;ncia ameboide. Sua morfologia ameboide causou, no passado, confus&#245;es taxon&#244;micas, mas a filogenia molecular esclareceu seu posicionamento evolutivo e ressaltou o uso compartilhado dos pseud&#243;podes, apesar das linhagens divergentes.
Este clado compreende linhagens diversas como Chlorarachniophyta, Radiolaria e Foraminifera, todas adaptadas a nichos ecol&#243;gicos distintos e que apresentam uma variedade de estrat&#233;gias metab&#243;licas.
Chlorarachniophyta
Chlorarachniophyta s&#227;o protistas fototr&#243;ficos unicelulares encontrados em ambientes marinhos e de &#225;gua doce. S&#227;o um exemplo de endossimbiose secund&#225;ria, na qual um hospedeiro eucari&#243;tico n&#227;o fotossint&#233;tico englobou um eucarioto algal fotossint&#233;tico. Diferentemente dos plast&#237;dios prim&#225;rios, que tipicamente possuem duas membranas, os cloroplastos das chlorarachniophyta s&#227;o circundados por quatro membranas e ret&#234;m um nucleomorfo&#8212;um n&#250;cleo vestigial da alga englobada. Esse nucleomorfo representa um raro estado intermedi&#225;rio na integra&#231;&#227;o do plast&#237;dio, preservando evid&#234;ncias gen&#244;micas e estruturais do evento endossimbi&#243;tico.
A arquitetura gen&#233;tica das chlorarachniophyta &#233; extraordinariamente complexa. Pelo menos cinco genomas est&#227;o presentes: (1) o genoma nuclear do hospedeiro, (2) o genoma mitocondrial do hospedeiro, (3) o genoma do nucleomorfo, (4) o genoma mitocondrial da alga, e (5) o genoma do plast&#237;dio. Ao longo da evolu&#231;&#227;o, muitos genes do endossimbionte foram transferidos para o n&#250;cleo do hospedeiro, resultando em uma redu&#231;&#227;o gen&#244;mica no nucleomorfo e no cloroplasto. Essa integra&#231;&#227;o gen&#244;mica reflete um processo evolutivo de otimiza&#231;&#227;o, no qual fun&#231;&#245;es redundantes s&#227;o eliminadas ou realocadas.
Foraminifera
Os foramin&#237;feros s&#227;o protistas marinhos ameboides que constroem carapa&#231;as elaboradas, frequentemente compostas por carbonato de c&#225;lcio. Essas carapa&#231;as n&#227;o fazem parte da c&#233;lula viva, mas fornecem prote&#231;&#227;o estrutural e sustentam a alimenta&#231;&#227;o por pseud&#243;podes. Os foramin&#237;feros bent&#244;nicos habitam o fundo oce&#226;nico, alimentando-se de mat&#233;ria org&#226;nica particulada e estabelecendo simbioses de troca de nutrientes com algas. Esp&#233;cies planct&#244;nicas abrigam endossimbiontes fototr&#243;ficos e ocupam as camadas superiores do oceano, onde a luz solar &#233; acess&#237;vel.
O potencial de fossiliza&#231;&#227;o das carapa&#231;as foramin&#237;feras as torna indispens&#225;veis na bioestratigrafia e na geologia do petr&#243;leo. Sua distribui&#231;&#227;o nos estratos geol&#243;gicos auxilia na infer&#234;ncia da idade relativa das camadas sedimentares e na avalia&#231;&#227;o do potencial de dep&#243;sitos de petr&#243;leo.
Radiolaria
Os radiol&#225;rios s&#227;o protistas marinhos planct&#244;nicos que habitam, principalmente, as &#225;guas superficiais. Seus esqueletos sim&#233;tricos &#224; base de s&#237;lica s&#227;o altamente ornamentados e permanecem ap&#243;s a morte, contribuindo para a forma&#231;&#227;o de lama silicosa no fundo do mar. Os radiol&#225;rios alimentam-se de detritos org&#226;nicos e bact&#233;rias, e por vezes estabelecem rela&#231;&#245;es simbi&#243;ticas com algas. Ao contr&#225;rio dos foramin&#237;feros, os radiol&#225;rios n&#227;o mant&#234;m endossimbiontes. Sua flutuabilidade &#233; mantida por inclus&#245;es lip&#237;dicas, vac&#250;olos e pseud&#243;podes r&#237;gidos que contrabalan&#231;am a tend&#234;ncia de afundamento gravitacional.

Diversidade Dos Protistas-III

Rhizaria s&#227;o um grupo diverso de protistas unicelulares caracterizados por suas extens&#245;es citoplasm&#225;ticas filamentosas conhecidas como ...

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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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