Radiolarians are planktonic protists with wide spatial and temporal distribution (throughout oceanic basins as well as through geological time). The protoplasmic body is divided in endoplasm and ectoplasm, the former related to reproductive functions and the latter to the regulation of the position in the water column, digestion and breathing. The endoplasm and the ectoplasm are separated by the capsular membrane, which is an exclusive characteristic of the group. Their skeletons are composed by amorphous silica, that enables their preservation in marine sediments deposited below de calcite compensation depth (CCD). These characteristics allow to apply fossil radiolarians to solve several problems in geosciences, as in paleobiogeography, paleogeographic reconstruction of tectonically complex areas, biostratigraphy and aleoceanography/paleoclimatology. Citation: Kochhann K.G.D. 2011. Radiolários: estado do conhecimento e aplicações às geociências.
