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. The elaborate mineral skeleton is usually made of silica.[1] 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 change as species, they represent an important diagnostic fossil found from the Cambrian onwards. Some common radiolarian fossils include Actinomma, Heliosphaera and Hexadoridium.

Temporal range: Cambrian – Recent
Radiolaria illustration from the Challenger Expedition 1873–76.
Scientific classification



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

Radiolarians have many needle-like pseudopods supported by bundles of microtubules, which aid in the radiolarian's buoyancy. The cell nucleus and most other organelles are in the endoplasm, while the ectoplasm is filled with frothy vacuoles and lipid droplets, keeping them buoyant. The radiolarian can often contain symbiotic algae, especially zooxanthellae, which provide most of the cell's energy. Some of this organization is found among the 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.


The radiolarians belong to the supergroup Rhizaria together with (amoeboid or flagellate) Cercozoa and (shelled amoeboid) Foraminifera.[2] Traditionally the radiolarians have been divided into four groups—Acantharea, Nassellaria, Spumellaria and Phaeodarea. Phaeodaria is however now considered to be a Cercozoan.[3][4] 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).[5][6]

There are several higher-order groups that have been detected in molecular analyses of environmental data. Particularly, groups related to Acantharia[7] and Spumellaria.[8] 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.[9] 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.[10] 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.[11]

Higher concentrations of dissolved carbon dioxide (CO
) 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.

Anthocyrtium hispidum Haeckel - Radiolarian (34986365113)
Anthocyrtium hispidum Haeckel


  1. ^ Smalley,I.J. 1963. Radiolarians:construction of spherical skeleton. Science 140, 396-397. doi:10.1126/science.140.3565.396
  2. ^ Pawlowski J, Burki F (2009). "Untangling the phylogeny of amoeboid protists". J. Eukaryot. Microbiol. 56 (1): 16–25. doi:10.1111/j.1550-7408.2008.00379.x. PMID 19335771.
  3. ^ 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. doi:10.1016/j.ejop.2005.06.001.
  4. ^ 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. doi:10.1073/pnas.0308602101. PMC 419558. PMID 15148395.
  5. ^ 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. doi:10.1371/journal.pone.0023526. PMC 3154480. PMID 21853146.
  6. ^ Cavalier-Smith T (December 1993). "Kingdom protozoa and its 18 phyla". Microbiol. Rev. 57 (4): 953–94. PMC 372943. PMID 8302218.
  7. ^ 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. doi:10.1016/j.protis.2011.10.002. PMID 22154393.
  8. ^ 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. doi:10.1111/j.1462-2920.2007.01247.x. PMID 17472637.
  9. ^ 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. doi:10.1111/j.1550-7408.1999.tb04614.x. PMID 18092388.
  10. ^ Braun, Chen, Waloszek & Maas (2007), "First Early Cambrian Radiolaria", in Vickers-Rich, Patricia; Komarower, Patricia (eds.), The Rise and Fall of the Ediacaran Biota, Special publications, 286, London: Geological Society, pp. 143–149, doi:10.1144/SP286.10, ISBN 9781862392335, OCLC 156823511CS1 maint: uses authors parameter (link)
  11. ^ Radiolarians

External links

  1. ^ Boltovskoy, Demetrio; Anderson, O. Roger; Correa, Nancy M. (2016). Archibald, John M.; Simpson, Alastair G. B.; Slamovits, Claudio H.; Margulis, Lynn; Melkonian, Michael; Chapman, David J.; Corliss, John O. (eds.). Handbook of the Protists. Springer International Publishing. pp. 1–33. doi:10.1007/978-3-319-32669-6_19-1. ISBN 9783319326696.

The Acantharea (Acantharia) are a group of radiolarian protozoa, distinguished mainly by their strontium sulfate skeletons.

Cana (radiolarian)

Cana is an extinct genus of prehistoric radiolarians in the extinct family Pantanelliidae. The species C. elegans is from the Cretaceous of Northwest Turkey.


Clathrocyclas is a genus of radiolarians in the family Theoperidae.


Collodaria is a unicellular order (organisms within the order are called Collodarians) under the phylum Radiozoa (or Radiolaria) and the infrakingdom Rhizaria. Like most of the Radiolaria taxonomy, Collodaria was first described by Ernst Haeckel, a German scholar who published three volumes of manuscript describing the extensive samples of Radiolaria collected by the voyage of HMS Challenger. Recent molecular phylogenetic studies concluded that there are Collodaria contains three families, Sphaerozodae, Collosphaeridae, and Collophidilidae.


D-Shape is a large 3-dimensional printer that uses binder-jetting, a layer by layer printing process, to bind sand with an inorganic seawater and magnesium-based binder in order to create stone-like objects. Invented by Enrico Dini, founder of Monolite UK Ltd, the first model of the D-Shape printer used epoxy resin, commonly used as an adhesive in the construction of skis, cars, and airplanes, as the binder. Dini patented this model in 2006. After experiencing problems with the epoxy, Dini changed the binder to the current magnesium-based one and patented his printer again in September 2008. In the future, Dini aims to use the printer to create full-scale buildings.

DSDP 368

The DSDP 368 was an area that was drilled as part of the Deep Sea Drilling Project that took place below the Cape Verde Rise.

Didymocyrtis (fungus)

Didymocyrtis is also a zoological genus of spumellarian Radiolaria.

Didymocyrtis is a genus of fungi in the class Dothideomycetes. The relationship of this taxon to other taxa within the class is unknown (incertae sedis). Also, the placement of this genus within the Dothideomycetes is uncertain.

Esther Aberdeen Holm

Esther Aberdeen Holm (January 6, 1904 – May 4, 1984) was an American academic who began as a paleontologist turning to applied geology.


Haeckelites are three-fold coordinated networks of carbon atoms generated by a periodic arrangement of pentagons, hexagons and heptagons. They were first proposed by Humberto and Mauricio Terrones and their colleagues in 2000. They were named in honour of Ernst Haeckel, whose diagrams of radiolaria contained similar structural features. They have not yet been synthesised in the laboratory, but have been the subject of a considerable amount of theoretical work.


Heliozoa, commonly known as sun-animalcules, are microbial eukaryotes (protists) with stiff arms (axopodia) radiating from their spherical bodies, which are responsible for their common name. The axopodia are microtubule-supported projections from the amoeboid cell body, and are variously used for capturing food, sensation, movement, and attachment. They are similar to Radiolaria, but they are distinguished from them by lacking central capsules and other complex skeletal elements, although some produce simple scales and spines. They may be found in both freshwater and marine environments.


Nassellaria is an order of Rhizaria belonging to the class Radiolaria. The organisms of this order are characterized by a skeleton cross link with a cone or ring.

Nodule (geology)

In sedimentology and geology, a nodule is small, irregularly rounded knot, mass, or lump of a mineral or mineral aggregate that typically has a contrasting composition, such as a pyrite nodule in coal, a chert nodule in limestone, or a phosphorite nodule in marine shale, from the enclosing sediment or sedimentary rock. Normally, a nodule has a warty or knobby surface and exists as a discrete mass within the host strata. In general, they lack any internal structure except for the preserved remnants of original bedding or fossils. Nodules are closely related to concretions and sometimes these terms are used interchangeably. Minerals that typically form nodules include calcite, chert, apatite (phosphorite), anhydrite, and pyrite.In sedimentology and geology, nodular is used to describe a sediment or sedimentary rock composed of scattered to loosely packed nodules in matrix of like or unlike character. It is also used to describe mineral aggregates that occur in the form of nodules, e.g. colloform mineral aggregate with a bulbed surface.Nodule is also used for widely scattered concretionary lumps of manganese, cobalt, iron, and nickel found on the floors of the world's oceans. This is especially true of manganese nodules. Manganese and phosphorite nodules form on the seafloor and are syndepositional in origin. Thus, technically speaking, they are concretions instead of nodules.Chert and flint nodules are often found in beds of limestone and chalk. They form from the redeposition of amorphous silica arising from the dissolution of siliceous spicules of sponges, or debris from radiolaria and the postdepositional replacement of either the enclosing limestone or chalk by this silica.


The Phaeodarea are a group of amoeboid Cercozoa. They are traditionally considered radiolarians, but in molecular trees do not appear to be close relatives of the other groups, and are instead placed among the Cercozoa. They are distinguished by the structure of their central capsule and by the presence of a phaeodium, an aggregate of waste particles within the cell.

The term "Radiozoa" has been used to refer to radiolaria when Phaeodarea is explicitly excluded.Phaeodarea produce hollow skeletons composed of amorphous silica and organic material, which rarely fossilize. The endoplasm is divided by a cape with three openings, of which one gives rise to feeding pseudopods, and the others let through bundles of microtubules that support the axopods. Unlike true radiolarians, there are no cross-bridges between them. They also lack symbiotic algae, generally living below the photic zone, and do not produce any strontium sulphate.


The polycystines are a group of radiolarians. They include the vast majority of the fossil radiolaria, as their skeletons are abundant in marine sediments, making them one of the most common groups of microfossils. These skeletons are composed of opaline silica. In some it takes the form of relatively simple spicules, but in others it forms more elaborate lattices, such as concentric spheres with radial spines or sequences of conical chambers.


For the brachiopod genus, see Retaria (brachiopod).

Retaria is a clade within the supergroup Rhizaria containing the Foraminifera and the Radiolaria. In 2019, the Retaria were recognized as a basal Rhizaria group, as sister of the Cercozoa.


The Rhizaria are a species-rich supergroup of mostly unicellular eukaryotes. Except from the Chlorarachniophyte and three species in the genus Paulinella, they are all non-photosyntethic. A multicellular form, Guttulinopsis vulgaris, a cellular slime mold, has also been described.

This supergroup was proposed by Cavalier-Smith in 2002. 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. 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.


The genus Stylodictya belongs to a group of organisms called the Radiolaria. Radiolarians are amoeboid protists found as zooplankton in oceans around the world and are typically identified by their ornate skeletons.

The Radiolarian Series

The Radiolarian Series is an album project by experimental jazz fusion trio Medeski Martin & Wood released in three installments in 2008-2009.

The project is atypical among studio albums because, in a reversal of the typical recording process, the band decided to compose and then develop the songs through a series of tours before recording the music in the studio.

In early 2008 the band announced on their official website: "Medeski Martin & Wood are planning three tours, plus three albums in 2008. Each tour and subsequent album will consist of all NEW MUSIC. The plan: Write > Tour > Record > Repeat." "The problem with us," keyboardist John Medeski explains, "is that when we record an album, by the time a record company gets it out, we’ve already been playing the music for six or eight months, and we’re ready to move on."The three volumes of The Radiolarian Series were first released as three separate albums. The series was also released as a 5-CD box set in 2009.

The Radiolarian Series takes its name from radiolarians (also radiolaria), amoeboid protozoa that produce intricate mineral skeletons, typically with a central capsule dividing the cell into inner and outer portions, called endoplasm and ectoplasm.

Radiolaria grow their intricately beautiful patterned skeleton around their soft core in defiance of normal biological process. This is, according to the band, "similar to Medeski Martin and Wood's latest creative cycle." The Radiolarian Series consists of music composed and developed over the course of the band's three-part 2008 "Viva la Evolution" Tour:

Part One: February 19–29 (Northeast U.S.)

Part Two: July 11–18 (Southeast U.S.)

Part Three: November 12–22 (Pacific Northwest (U.S. & Canada))

Tobago Volcanic Group

The Tobago Volcanic Group is a geologic group in Trinidad and Tobago. It preserves radiolaria and ammonite fossils dating back to the Albian period. The formation contains the Bacolet Formation and comprises organic-rich, black pyritic siliceous mudstones and fine-grained volcaniclastic sandstones and siltstones.

Incertae sedis
Extant life phyla/divisions by domain


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