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Radiolaria

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Title: Radiolaria  
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Subject: Silicon, Cercozoa, Acantharea, Polycystine, Sticholonche
Collection: Amoeboids, Cambrian First Appearances, Radiolarians
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Radiolaria

Radiolaria
Temporal range: Cambrian – Recent
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Radiolaria illustration from the Challenger Expedition 1873–76.
Scientific classification
Domain: Eukaryota
(unranked): SAR
(unranked): Rhizaria
Phylum: Retaria
Subphylum: Radiozoa
Cavalier-Smith, 1987
Classes

Polycystinea
Acantharea
Sticholonchea (formerly in Heliozoa)
Excluded: Phaeodaria (now in Cercozoa)

The Radiolaria, also called Radiozoa, are protozoa of (diameter 0.1–0.2 mm) that produce intricate mineral skeletons, typically with a central capsule dividing the cell into the inner and outer portions of endoplasm and ectoplasm. They are found as zooplankton throughout the ocean, and their skeletal remains make up a large part of the cover of the ocean floor as siliceous ooze. Due to their rapid turn-over of species, they represent an important diagnostic fossil found from the Cambrian onwards. Some common radiolarian fossils include Actinomma, Heliosphaera and Hexadoridium.

Contents

  • Description 1
  • Taxonomy 2
  • Fossil record 3
  • Haeckel's radiolarians 4
  • References 5
  • External links 6

Description

Circogonia icosahedra, a species of Radiolaria, shaped like a regular icosahedron

Radiolarians have many needle-like heliozoa, but those lack central capsules and only produce simple scales and spines.

Some radiolarians are known for their resemblance to regular polyhedra, such as the icosahedron-shaped Circogonia icosahedra pictured to the left.

Taxonomy

The radiolarians belongs to the supergroup Rhizaria together with (amoeboid or flagellate) Cercozoa and (shelled amoeboid) Foraminifera.[1] Traditionally the radiolarians have been divided into four groups—Acantharea, Nassellaria, Spumellaria and Phaeodaria. Phaeodaria is however now considered to be a Cercozoan.[2][3] Nassellaria and Spumellaria both produce siliceous skeletons and were therefore grouped together in the group Polycystina. Despite some initial suggestions to the contrary, this is also supported by molecular phylogenies. The Acantharea produce skeletons of strontium sulfate and is closely related to a peculiar genus, Sticholonche (Taxopodida), which lacks an internal skeleton and was for long time considered a heliozoan. The Radiolaria can therefore be divided into two major lineages: Polycystina (Spumellaria + Nassellaria) and Spasmaria (Acantharia + Taxopodida).[4][5]

There are several higher-order groups that have been detected in molecular analyses of environmental data. Particularly, groups related to Acantharia[6] and Spumellaria.[7] These groups are so far completely unknown in terms of morphology and physiology and the radiolarian diversity is therefore likely to be much higher than what is currently known.

The relationship between the Foraminifera and Radiolaria is also debated. Molecular trees supports their close relationship—a grouping termed Retaria.[8] But whether they are sister lineages or if the Foraminifera should be included within the Radiolaria is not known.

Fossil record

The earliest known radiolaria date to the very start of the Cambrian period, appearing in the same beds as the first small shelly fauna—they may even be terminal Precambrian in age. They have significant differences from later radiolaria, with a different silica lattice structure and few, if any, spikes on the test.[9] Ninety percent of radiolarian species are extinct. The skeletons, or tests, of ancient radiolarians are used in geological dating, including for oil exploration and determination of ancient climates.[10]

Higher concentrations of dissolved carbon dioxide (CO2) in sea water dissolves their fine skeletons made of silica, destroying their delicate structure, seen as fractured scattered pieces under a microscope. This is linked to periods of heightened volcanic activity.

Haeckel's radiolarians

German biologist Ernst Haeckel produced finely detailed drawings of radiolaria in Kunstformen der Natur (1904), helping to popularize these protists among Victorian parlor microscopists alongside foraminifera and diatoms, in addition to two lengthy illustrated monographs from field observation dedicated to Radiolaria, intended for academic study.

Proteus: A Nineteenth Century Vision, written and directed by David Lebrun, is an animated documentary focusing on Radiolaria, making extensive use of Haeckel's drawings.[11]

References

  1. ^ Pawlowski J, Burki F (2009). "Untangling the phylogeny of amoeboid protists". J. Eukaryot. Microbiol. 56 (1): 16–25.  
  2. ^ Yuasa T, Takahashi O, Honda D, Mayama S (2005). "Phylogenetic analyses of the polycystine Radiolaria based on the 18s rDNA sequences of the Spumellarida and the Nassellarida". European Journal of Protistology 41 (4): 287–298.  
  3. ^ 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.  
  4. ^ Krabberød AK, Bråte J, Dolven JK, et al. (2011). "Radiolaria divided into Polycystina and Spasmaria in combined 18S and 28S rDNA phylogeny". PLoS ONE 6 (8): e23526.  
  5. ^ Cavalier-Smith T (December 1993). "Kingdom protozoa and its 18 phyla". Microbiol. Rev. 57 (4): 953–94.  
  6. ^ Decelle J, Suzuki N, Mahé F, de Vargas C, Not F (May 2012). "Molecular phylogeny and morphological evolution of the Acantharia (Radiolaria)". Protist 163 (3): 435–50.  
  7. ^ Not F, Gausling R, Azam F, Heidelberg JF, Worden AZ (May 2007). "Vertical distribution of picoeukaryotic diversity in the Sargasso Sea". Environ. Microbiol. 9 (5): 1233–52.  
  8. ^ Cavalier-Smith T (July 1999). "Principles of protein and lipid targeting in secondary symbiogenesis: euglenoid, dinoflagellate, and sporozoan plastid origins and the eukaryote family tree". J. Eukaryot. Microbiol. 46 (4): 347–66.  
  9. ^ Braun, Chen, Waloszek & Maas (2007), "First Early Cambrian Radiolaria", in Vickers-Rich, Patricia; Komarower, Patricia, The Rise and Fall of the Ediacaran Biota, Special publications 286, London: Geological Society, pp. 143–149,  
  10. ^ Radiolarians
  11. ^ Lebrun, David (Director) (2004). Proteus: A Nineteenth Century Vision (DVD).  
  • Zettler, Linda A.; Sogin, ML; Caron, DA (1997). "Phylogenetic relationships between the Acantharea and the Polycystinea: A molecular perspective on Haeckel's Radiolaria". Proc. Natl. Acad. Sci. U.S.A. 94 (21): 11411–6.  
  • López-García P, Rodríguez-Valera F, Moreira D (January 2002). "Toward the monophyly of Haeckel's radiolaria: 18S rRNA environmental data support the sisterhood of polycystinea and acantharea". Mol. Biol. Evol. 19 (1): 118–121.  
  • Adl SM, Simpson AG, Farmer MA, et al. (2005). "The New Higher Level Classification of Eukaryotes with Emphasis on the Taxonomy of Protists". J. Eukaryot. Microbiol. 52 (5): 399–451.  
  • Haeckel, Ernst (2005). Art Forms from the Ocean: The Radiolarian Atlas of 1862. Munich; London: Prestel Verlag.  

External links

  • Radiolarians
  • Brodie, C. (February 2005). "Geometry and Pattern in Nature 3: The holes in radiolarian and diatom tests". Micscape (Microscopy-UK) (112).  
  • Radiolaria.org
  • Haeckel, Ernst (1862). )Rhizopoda radiariaDie Radiolarien (. Berlin. 
  • Radiolaria—Droplet
  • Tree Of Life—Radiolaria
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