A subclass of protozoa (class Actinopodea) which possess more or less elaborate skeletons of silica. Most are pelagic marine organisms. Radiolarian fossils have been found in Cambrian rocks and they are important stratigraphic fossils for Mesozoic and Cenozoic deep-sea sediments. See radiolarian earth; radiolarian ooze.
Subjects: Biological Sciences — Earth Sciences and Geography.