What is Radiolaria?
[[File:Haeckel Stephoidea.jpg|thumb|right|250px|A group illustration of one of the <br/>Radiolarian superfamilies (from Haekel).]] '''Radiolaria''' are [[amoeba|amoeboid]] [[protist]]s which produce [[mineral]] [[skeleton]]s. The skeletons, usually of [[silica]] (SiO<sub>2</sub>), have a central capsule. This divides the cell into inner and outer portions, called ''endoplasm'' and ''ectoplasm''. Radiolaria are found as [[zooplankton]] throughout the ocean, and their skeletal remains cover large portions of the ocean floor as '''radiolarian ooze'''. Radiolaria have existed since the beginning of the [[Palaeozoic]] [[era]].<ref>[http://www.radiolaria.org/what_are_radiolarians.htm Kling, Stanley A. and Boltovskoy, Demetrio, 2002. What are Radiolarians?]</ref> They take their name from the radial [[symmetry]] of most species. They are valuable markers or [[diagnosis|diagnostic]] [[fossil]]s, because they have a rapid turn-over of [[species]]. This helps to identify strata, and to correlate [[strata]] at different sites. Radiolaria are heterotrophs (eat other things), but also may include [[protist]] [[algae]] as [[endosymbiosis|endosymbionts]]. == Structure == The skeletons of radiolarians are generally organized around spicules, or spines, which extend from the main skeletal mass. Formed from the fusion of many of these spines is the outermost skeleton, the shell or ''test''. Connecting this shell to the many concentrically organized inner shells are bars or beams, which strengthen and support the structure.<ref>Hooper Museum (Ben Barnes 2001) [http://hoopermuseum.earthsci.carleton.ca/2001_radiolarians_bb/ Radiolarians]</ref> The [[Cell nucleus|nuclei]] and most other [[organelle]]s are in the endoplasm, while the ectoplasm is filled with frothy vacuoles and lipid droplets, keeping them buoyant. Often it also contains [[symbiosis|symbiotic]] algae which provide much of the cell's energy. Not much is known about the living amoebae because they cannot be cultured in the [[laboratory]]. <gallery> |Radiolaria ske