Radiolaria (superclass Sarcodina, class Actinopodea) A subclass of protozoa which possess more or less elaborate skeletons of silica. The cell body is generally spherical with axopodia radiating from the periphery. Many species are known. They are chiefly pelagic marine organisms. Fossil radiolarians have been found in Cambrian rocks and they are important stratigraphic fossils for Mesozoic and Cenozoic deep-sea sediments.

Radiolaria 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 and radiolarian ooze.

Radiolaria A large group of marine sarcodinids (protists), characterized by having a shell with a perforated, membraneous capsule containing the endoplasm, and a siliceous or strontium sulphate skeleton consisting of a lattice shape of variable morphology made up of spicules, bars, and spines. Radiolarians live mainly in surface waters and the earliest forms are Cambrian in age. They are used in the biostratigraphic correlation of oceanic sediments, particularly where calcareous microfossils have been dissolved.