radiolaria radiolaria 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. they are found as zooplankton throughout the global ocean. as zooplankton, radiolarians are primarily heterotrophic, but many have photosynthetic endosymbionts and are, therefore, considered mixotrophs. the skeletal remains of some types of radiolarians make up a large part of the cover of the ocean floor as siliceous ooze. due to their rapid change as species and intricate skeletons, radiolarians represent an important diagnostic fossil found from the cambrian onwards. radiolariatemporal range: radiolaria illustration from the challenger expedition 1873–76 scientific classification domain: eukaryota clade: diaphoretickes clade: sar phylum: retaria subphylum: radiolariacavalier-smith, 1987 classes polycystinea nassellaria spumellaria collodaria acantharea taxopodida (sticholonche) excluded: phaeodaria (now in cercozoa) part of a series onplankton trophic mode phytoplankton zooplankton mixoplankton mycoplankton bacterioplankton virioplankton by size heterotrophic picoplankton microalgae microzooplankton nanophytoplankton calcareous photosynthetic picoplankton picoeukaryote picoplankton marine microplankton by taxonomy algae diatoms coccolithophores dinoflagellates protozoans radiolarians foraminiferans amoebae ciliates bacteria cyanobacteria archaea viruses by habitat aeroplankton geoplankton marine plankton prokaryotes protists freshwater plankton other types gelatinous zooplankton holoplankton ichthyoplankton meroplankton pseudoplankton tychoplankton blooms algal bloom critical depth cyanobacterial bloom harmful algal bloom spring bloom eutrophication great atlantic sargassum belt great calcite belt milky seas effect related topics algaculture claw hypothesis cpr diel vertical migration f-ratio marine primary production ocean fertilization iron paradox of the plankton planktivore planktology thin layers naames category description 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 below. taxonomy the radiolarians belong to the supergroup rhizaria together with (amoeboid or flagellate) cercozoa and (shelled amoeboid) foraminifera. traditionally the radiolarians have been divided into four groups—acantharea, nassellaria, spumellaria and phaeodarea. phaeodaria is however now considered to be a cercozoan. 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). there are several higher-order groups that have been detected in molecular analyses of environmental data. particularly, groups related to acantharia and spumellaria. 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 support their close relationship—a grouping termed retaria. but whether they are sister lineages or whether the foraminifera should be included within the radiolaria is not known. class order image families genera species description polycystinea nassellaria ... spumellaria ... collodaria ... acantharea ... sticholonchea taxopodida 1 1 1 ... biogeography radiolarian biogeography with observed and predicted responses to temperature change the color polygons in all three panels represent generalized radiolarian biogeographic provinces, as well as their relative water mass temperatures (cooler colors indicate cooler temperatures, and vice versa). globe image adapted from nasa blue marble: next generation imagery. ocean floor bathymetry from google earth seafloor elevation profile (5°n–74°s, at 120°w). in the diagram on the right, a illustrates generalized radiolarian provinces and their relationship to water mass temperature (warm versus cool color shading) and circulation (gray arrows). due to high-latitude water mass submergence under warm, stratified waters in lower latitudes, radiolarian species occupy habitats at multiple latitudes, and depths throughout the world oceans. thus, marine sediments from the tropics reflect a composite of several vertically stacked faunal assemblages, some of which are contiguous with higher latitude surface assemblages. sediments beneath polar waters include cosmopolitan deep-water radiolarians, as well as high-latitude endemic surface water species. stars in (a) indicate the latitudes sampled, and the gray bars highlight the radiolarian assemblages included in each sedimentary composite. the horizontal purple bars indicate latitudes known for good radiolarian (silica) preservation, based on surface sediment composition. data show that some species were extirpated from high latitudes but persisted in the tropics during the late neogene, either by migration or range restriction (b). with predicted global warming, modern southern ocean species will not be able to use migration or range contraction to escape environmental stressors, because their preferred cold-water habitats are disappearing from the globe (c). however, tropical endemic species may expand their ranges toward midlatitudes. the color polygons in all three panels represent generalized radiolarian biogeographic provinces, as well as their relative water mass temperatures (cooler colors indicate cooler temperatures, and vice versa). circogonia icosahedra, radiolarian species shaped like a regular icosahedron anthocyrtium hispidum haeckel radiolarian shells radiolarian shapes drawings by haeckel 1904 (click for details)