- any minute, marine protozoan of the class Radiolaria, or, in some classification schemes, the superclass Actinopoda, having an amebalike body with radiating, filamentous pseudopodia and a usually elaborate outer skeleton.
- any of various marine protozoans constituting the order Radiolaria, typically having a siliceous shell and stiff radiating cytoplasmic projections: phylum Actinopoda (actinopods)
