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Rhizaria

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Title: Rhizaria  
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Subject: Eukaryote, Cabozoa, Cercozoa, Protozoa, SAR supergroup
Collection: Neoproterozoic First Appearances, Rhizaria
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Rhizaria

Rhizaria
Temporal range: Neoproterozoic - Recent
Live Ammonia tepida
Scientific classification
Domain: Eukaryota
(unranked): SAR
(unranked): Rhizaria
Cavalier-Smith, 2002
Phyla

Cercozoa
Retaria

Foraminifera
Radiolaria

The Rhizaria are a species-rich supergroup of mostly unicellular[1] eukaryotes.[2] A multicellular form has recently been described.[3] This supergroup was proposed by Cavalier-Smith in 2002. They vary considerably in form, but for the most part they are amoeboids with filose, reticulose, or microtubule-supported pseudopods. Many produce shells or skeletons, which may be quite complex in structure, and these make up the vast majority of protozoan fossils. Nearly all have mitochondria with tubular cristae.

Contents

  • Groups 1
  • Evolutionary relationships 2
  • References 3
  • External links 4

Groups

There are three main groups of Rhizaria:[4]

A few other groups may be included in the Cercozoa, but on some trees appear closer to the Foraminifera. These are the Phytomyxea and Ascetosporea, parasites of plants and animals respectively, and the peculiar amoeba Gromia. The different groups of Rhizaria are considered close relatives based mainly on genetic similarities, and have been regarded as an extension of the Cercozoa. The name Rhizaria for the expanded group was introduced by Cavalier-Smith in 2002,[5] who also included the centrohelids and Apusozoa.

Another order that appears to belong to this taxon is the Mikrocytida.[6] These are parasites of oysters.

Evolutionary relationships

Rhizaria are part of the bikont clade along with Archaeplastida, Chromalveolata, Excavata, and some smaller, unresolved groups such as Apusozoa and Centrohelida. As bikonts, they all descend from a heterotrophic eukaryote ancestor with two flagella.

Historically, many rhizarians were considered animals because of their motility and heterotrophy. However, when a simple animal-plant dichotomy was superseded by a recognition of additional kingdoms, taxonomists generally placed rhizarians in the kingdom Protista. When scientists began examining the evolutionary relationships among eukaryotes using molecular data, it became clear that the kingdom Protista was paraphyletic. Rhizaria appear to share a common ancestor with Stramenopiles and Alveolates forming part of the SAR (Stramenopiles+Alveolates+Rhizaria) super assemblage.[7] Rhizaria has been supported by molecular phylogenetic studies as a monophyletic group.[8]

References

  1. ^ Christopher Taylor (2004). "Rhizaria". 
  2. ^ Nikolaev SI, Berney C, Fahrni JF, et al. (May 2004). "The twilight of Heliozoa and rise of Rhizaria, an emerging supergroup of amoeboid eukaryotes". Proc. Natl. Acad. Sci. U.S.A. 101 (21): 8066–71.  
  3. ^ Brown; et al. (2012). "Aggregative Multicellularity Evolved Independently in the Eukaryotic Supergroup Rhizaria". 
  4. ^ Moreira D, von der Heyden S, Bass D, López-García P, Chao E, Cavalier-Smith T (July 2007). "Global eukaryote phylogeny: Combined small- and large-subunit ribosomal DNA trees support monophyly of Rhizaria, Retaria and Excavata". Mol. Phylogenet. Evol. 44 (1): 255–66.  
  5. ^  
  6. ^ Hartikainen, H; Stentiford, GD; Bateman, KS; Berney, C; Feist, SW; Longshaw, M; Okamura, B; Stone, D; Ward, G; Wood, C; Bass, D (2014). "Mikrocytids are a broadly distributed and divergent radiation of parasites in aquatic invertebrates". Curr Biol 24 (7): 807–12.  
  7. ^ Burki, F; Shalchian-Tabrizi, K; Minge, M; Skjaeveland, A; Nikolaev, SI; Jakobsen, KS; Pawlowski, J (2007). Butler, Geraldine, ed. "Phylogenomics Reshuffles the Eukaryotic Supergroups".  
  8. ^ Burki, Fabien; Shalchian-Tabrizi, Kamran; Pawlowski, Jan (August 23, 2008). "Phylogenomics reveals a new ‘megagroup’ including most photosynthetic eukaryotes". Biology Letters 4 (4): 366–9.  

External links

  • Molecular Phylogeny of Amoeboid Protists - Tree of Rhizaria
  • Tree of Life Eukaryotes
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