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.
Radiolaria are protozoa distinguished 1) by segregation of their soft anatomy into the central capsule, containing the endoplasm, and the surrounding ectoplasm (or calymma), and 2) by their siliceous (opaline) skeletons of the large majority of species. Also to be found are mitochondria (fewer than in the central capsule), digestive vacuoles, and algal symbionts. The ectoplasm extends into a complex network of pseudopodia, including irregular rhizopodia, radial axopodia (stiffened by axial rods), and delicate filpodia. Radiolaria are amoeboid protists which produce mineral skeletons. The skeletons, usually of silica (SiO 2), 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. They take their name from the radial symmetry of most species. They are valuable markers or diagnostic fossils, because they have a rapid turn-over of species. This helps to identify strata, and to correlate strata at different sites Introduction to the Radiolaria. With their glassy skeletons of often perfect geometric form and symmetry, radiolarians are among the most beautiful of all protists. They are also an ancient group, going back all the way to the early Cambrian Period.  Radiolarians have many needle-like pseudopodia 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. 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. First recorded occurrences of Radiolaria are from the latest Pre-Cambrian, they are generally thought to have been restricted to shallow water habitats. By the Silurian deep water forms are believed to have evolved. The following images are of a representative selection of Radiolaria aimed at giving a general overview of the different morphotypes. Each specimen is given a generic and, if possible, a species name followed by its age range, the site location from which the sample was obtained and its size in microns. 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 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. Radiolaria.org. Radiolaria.org is an online database containing information about radiolarians-fossil and recent, with images, descriptions, references, synonyms and links to other online resources. more ...  Radiolaria have an internal skeleton, consisting of a leathery central capsule that is usually perforated by numerous pores through which the intracapsular and extracapsular cytoplasms communicate. The capsule contains endoplasm with one or more nuclei and an internal layer of ectoplasm. In certain modern systems, the Radiolaria are subdivided into two classes, Polycystinea and Phaeodarea. Radiolarians occur almost exclusively in the open ocean as part of the plankton community, and are widely recognized for their ornate siliceous skeletons produced by most of the groups (illus. a – c). Radiolaria are planktonic protists. They are among the few protistan groups with comprehensive fossil records available for study. Radiolaria first appeared in the latter stages of the Pre-Cambrian period, one of the earliest microorganisms. It is believed that at first, these organisms only lived in shallow water. There are two major classifications of Radiolaria. The first, Polycystines, have simple skeletons that consist of simple opaline silica. The second, Phaeodarians, have more complex skeletons that consist of a siliceous composition. Phaeodarian skeletons are hollow, and are rarely preserved, as they dissolve in seawater. Introduction. Radiolaria are holoplanktonic protozoa and form part of the zooplankton, they are non-motile (except when flagella-bearing reproductive swarmers are produced) but contain buoyancy enhancing structures; they may be solitary or colonial. The following images are of a representative selection of Radiolaria aimed at giving a general overview of the different morphotypes. Each specimen is given a generic and, if possible, a species name followed by its age range, the site location from which the sample was obtained and its size in microns.
http://www.radiolaria.org/what_are_radiolarians.htm https://simple.wikipedia.org/wiki/Radiolaria http://www.ucmp.berkeley.edu/protista/radiolaria/rads.html https://en.wikipedia.org/wiki/Radiolaria http://www.ucl.ac.uk/GeolSci/micropal/radiolaria.html https://en.wikipedia.org/wiki/Radiolaria http://radiolaria.org/ http://encyclopedia2.thefreedictionary.com/Radiolaria http://microbewiki.kenyon.edu/index.php/Radiolaria http://www.ucl.ac.uk/GeolSci/micropal/radiolaria.html
what are radiolaria