Biology:Rhizaria

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The Rhizaria are a diverse and species-rich clade of mostly unicellular[1] eukaryotes.[2] Except for the chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are all non-photosynthetic, but many Foraminifera and Radiolaria have a symbiotic relationship with unicellular algae.[3] A multicellular form, Guttulinopsis vulgaris, a cellular slime mold, has been described.[4] This group was used by Cavalier-Smith in 2002, although the term "Rhizaria" had been long used for clades within the currently recognized taxon.

Being described mainly from rDNA sequences, they vary considerably in form, having no clear morphological distinctive characters (synapomorphies), but for the most part they are amoeboids with filose, reticulose, or microtubule-supported pseudopods. In the absence of an apomorphy, the group is ill-defined, and its composition has been very fluid. Some Rhizaria possess mineral exoskeletons (thecae or loricas), which are in different clades within Rhizaria made out of opal (SiO
2), celestite (SrSO
4), or calcite (CaCO
3).

Certain species can attain sizes of more than a centimeter with some species being able to form cylindrical colonies approximately 1 cm in diameter and greater than 1 m in length. They feed by capturing and engulfing prey with the extensions of their pseudopodia; forms that are symbiotic with unicellular algae contribute significantly to the total primary production of the ocean.[5]

Groups

The three main groups of Rhizaria are:[6]

A few other groups may be included in the Cercozoa, but 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,[7] who also included the centrohelids and Apusozoa.

A noteworthy order that belongs to Ascetosporea is the Mikrocytida.[8] These are parasites of oysters. This includes the causative agent of Denman Island Disease, Mikrocytos mackini a small (2−3 μm diameter) amitochondriate protistan.[9]

History

Similarities between various Rhizaria organisms have been noticed since the 19th century. In his 1861 classification of the Rhizopoda (amoebae), the zoologist William B. Carpenter proposed the order Reticularia, which consisted of Foraminifera and Gromiida on the basis of their very similar thin, reticulose pseudopodia with granules circulating inside.[10] However, the idea that these organisms and others such as Radiolaria were all related to one another emerged rather recently, with the help of molecular phylogenetics and advanced microscopy techniques in the late 20th century.[11]

Evolutionary relationships

Rhizaria are part of the SAR supergroup (Stramenopiles, Alveolates, Rhizaria), a grouping that had been presaged in 1993 through a study of mitochondrial morphologies.[12] SAR is currently placed in the Diaphoretickes along with Archaeplastida, Cryptista, Haptista, and several minor clades.

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 amoebae in the kingdom Protista. When scientists began examining the evolutionary relationships among eukaryotes in the 1970s, 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 super assemblage.[13] Rhizaria has been supported by molecular phylogenetic studies as a monophyletic group.[14] Biosynthesis of 24-isopropyl cholestane precursors in various rhizaria[15] suggests a relevant ecological role already during the Ediacaran.

Phylogeny

Rhizaria is a monophyletic group composed of three phyla: Cercozoa, Endomyxa, and Retaria.[16][17][18] The following cladogram depicts the evolutionary relationships between the major rhizarian classes, and is based on phylogenomic analyses published between 2018 and 2026.[19][20] In the last analysis, classes Sarcomonadea and Imbricatea were not monophyletic.[21]

Rhizaria
 
 
Cercozoa
 
Monadofilosa
 
 
 
 
 

Thecofilosea 50px

 
 

Thaumatomonadida (Imbricatea in part)

 
 
 
 

Micrometopion

 
 

Marimonadida

 
 
 
 
 

Pediglissa (Sarcomonadea in part)

 
 

Euglyphida (Imbricatea in part) 40px

 
 
 
 

Sainouroidea

 
 
 

Paracercomonada (Sarcomonadea in part)

 
 
 
 

Granofilosea (Reticulofilosa in part)

 
 

Chlorarachnea (Reticulofilosa in part) 50px

 
(Filosa)
 
 
 
Endomyxa
 
 

Apofilosa 50px

 
 

Ascetosporea 50px

 
 
 
 

Vampyrellida 50px

 
 

Phytomyxea 70px

 
 
 
 
 

Skiomonadea

 
 
 
 
Retaria
Foraminifera
 

Globothalamea

 
 

Tubothalamea

 
 

Monothalamea

 
 
Radiolaria
 
 

Acantharea

 
 

Sticholonchea

 
 
 

Polycystinea

 
 
 
 
 

Sexual cycle

Complete sexual life cycles have been demonstrated for two lineages (Foraminifera and Gromia) and direct evidence for karyogamy or meiosis has been observed in five lineages (Euglyphida, Thecofilosea, Chlorarachniophyta, Plasmodiophorida and Phaeodarea).[22] In particular, the Foraminifera are marine amoebae that are defined by a dynamic network of pseudopodia, and the production of intricate shells.[22] These amoeba have complex sexual life cycles with meiosis and gamete production occurring at separate stages.[22]

References

  1. ↑ Taylor, Christopher (2004). "Rhizaria". http://www.palaeos.com/Eukarya/Units/Rhizaria/Rhizaria.html. 
  2. ↑ Nikolaev, Sergey I.; Berney, Cédric; Fahrni, José F. et al. (May 2004). "The twilight of Heliozoa and rise of Rhizaria, an emerging supergroup of amoeboid eukaryotes". PNAS 101 (21): 8066–71. doi:10.1073/pnas.0308602101. PMID 15148395. 
  3. ↑ Gast, Rebecca J.; Caron, David A. (2001-10-01). "Photosymbiotic associations in planktonic foraminifera and radiolaria". Hydrobiologia 461 (1): 1–7. doi:10.1023/A:1012710909023. Bibcode: 2001HyBio.461....1G. 
  4. ↑ Brown, Matthew W.; Kolisko, Martin; Silberman, Jeffrey D.; Roger, Andrew J. (June 2012). "Aggregative Multicellularity Evolved Independently in the Eukaryotic Supergroup Rhizaria". Current Biology 22 (12): 1123–7. doi:10.1016/j.cub.2012.04.021. PMID 22608512. Bibcode: 2012CBio...22.1123B. 
  5. ↑ "Ocean science: The rise of Rhizaria". Nature 532 (7600): 444–5. April 2016. doi:10.1038/nature17892. PMID 27096370. Bibcode: 2016Natur.532..444C. 
  6. ↑ "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. July 2007. doi:10.1016/j.ympev.2006.11.001. PMID 17174576. Bibcode: 2007MolPE..44..255M. 
  7. ↑ Cavalier-Smith, Thomas (2002). "The phagotrophic origin of eukaryotes and phylogenetic classification of Protozoa". International Journal of Systematic and Evolutionary Microbiology 52 (2): 297–354. doi:10.1099/00207713-52-2-297. PMID 11931142. http://ijs.sgmjournals.org/cgi/content/abstract/52/2/297. Retrieved 2007-06-08. 
  8. ↑ Hartikainen, H.; Stentiford, G.D.; Bateman, K.S.; Berney, C.; Feist, S.W.; Longshaw, M.; Okamura, B.; Stone, D. et al. (2014). "Mikrocytids are a broadly distributed and divergent radiation of parasites in aquatic invertebrates". Curr Biol 24 (7): 807–12. doi:10.1016/j.cub.2014.02.033. PMID 24656829. Bibcode: 2014CBio...24..807H. https://nhm.openrepository.com/bitstream/10141/622246/1/Mikrocytids_CurrBiol_2014.pdf. 
  9. ↑ Hine, P.M.; Bower, S.M.; Meyer, G.R.; Cochennec-Laureau, N.; Berthe, F.C.J. (2001). "Ultrastructure of Mikrocytos mackini, the cause of Denman Island disease in oysters Crassostrea spp. and Ostrea spp. in British Columbia, Canada". Diseases of Aquatic Organisms 45 (3): 215–227. doi:10.3354/dao045215. PMID 11558731. http://www.int-res.com/abstracts/dao/v45/n3/p215-227/. 
  10. ↑ Carpenter, William Benjamin (1861). "XLVII.-On the systematic arrangement of the Rhizopoda". Natural History Review (Dublin and London) 1 (4): 478. https://www.biodiversitylibrary.org/item/30158#page/478/mode/1up. 
  11. ↑ "Rhizaria". Current Biology 24 (3): R103–7. February 2014. doi:10.1016/j.cub.2013.12.025. PMID 24502779. Bibcode: 2014CBio...24.R103B. 
  12. ↑ "[The basic types and forms of the fine structure of mitochondrial cristae: the degree of their evolutionary stability (capacity for morphological transformations)]" (in Russian). Tsitologiia 35 (4): 3–34. 1993. PMID 8328023. 
  13. ↑ Burki, F.; Shalchian-Tabrizi, K.; Minge, M.; Skjaeveland, A.; Nikolaev, S.I.; Jakobsen, K.S.; Pawlowski, J. (2007). Butler, Geraldine. ed. "Phylogenomics Reshuffles the Eukaryotic Supergroups". PLoS ONE 2 (8): e790–. doi:10.1371/journal.pone.0000790. PMID 17726520. Bibcode: 2007PLoSO...2..790B. 
  14. ↑ 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. doi:10.1098/rsbl.2008.0224. PMID 18522922. 
  15. ↑ Hallmann, Christian; Stuhr, Marleen; Kucera, Michal et al. (2019-03-04). "Putative sponge biomarkers in unicellular Rhizaria question an early rise of animals". Nature Ecology & Evolution 3 (4): 577–581. doi:10.1038/s41559-019-0806-5. PMID 30833757. Bibcode: 2019NatEE...3..577N. 
  16. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Adl-2019
  17. ↑ Bass, D. et al. (February 2009). "Phylogeny of Novel Naked Filose and Reticulose Cercozoa: Granofilosea cl. n. and Proteomyxidea Revised". Protist 160 (1): 75–109. doi:10.1016/j.protis.2008.07.002. PMID 18952499. 
  18. ↑ >Howe, Alexis T.; Bass, David; Scoble, Josephine M. et al. (2011). "Novel Cultured Protists Identify Deep-branching Environmental DNA Clades of Cercozoa: New Genera Tremula, Micrometopion, Minimassisteria, Nudifila, Peregrinia". Protist 162 (2): 332–372. doi:10.1016/j.protis.2010.10.002. PMID 21295519. 
  19. ↑ Cavalier-Smith, Thomas; Chao, Ema E .; Lewis, Rhodri (April 2018). "Multigene phylogeny and cell evolution of chromist infrakingdom Rhizaria: contrasting cell organisation of sister phyla Cercozoa and Retaria". Protoplasma 255 (5): 1517–1574. doi:10.1007/s00709-018-1241-1. PMID 29666938. Bibcode: 2018Prpls.255.1517C. 
  20. ↑ Irwin, Nicholas A. T.; Tikhonenkov, Denis V.; Hehenberger, Elisabeth et al. (2019-01-01). "Phylogenomics supports the monophyly of the Cercozoa". Molecular Phylogenetics and Evolution 130: 416–423. doi:10.1016/j.ympev.2018.09.004. PMID 30318266. Bibcode: 2019MolPE.130..416I. 
  21. ↑ Lax, Gordon; Cooney, Elizabeth C.; Zlatogursky, Vasily; Mtawali, Mahara; Okamoto, Noriko et al. (30 January 2026). "Phylogenomic tree of Cercozoa based on single-cell transcriptomes from 100 uncultured cells". BMC Biology 24 (1). doi:10.1186/s12915-026-02536-4. ISSN 1741-7007. PMID 41618358. 
  22. ↑ 22.0 22.1 22.2 "The chastity of amoebae: re-evaluating evidence for sex in amoeboid organisms". Proc Biol Sci 278 (1715): 2081–90. July 2011. doi:10.1098/rspb.2011.0289. PMID 21429931. 

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