Assembly of the radiolarian Actinomma drymodes, illustration. A. drymodes is a spherical radiolarian with a skeleton consisting of two concentric spheres with pores in it connected by needle-like spikes. Radiolaria are small protozoa with a mineral skeleton of silica. They are part of the marine plankton. They trap other planktonic organisms with pseudopodia that protrude through the pores.