Radiolaria. Coloured scanning electron micrograph (SEM) of the shells of various radiolaria. Radiolaria are single-celled protozoans that are found in marine plankton. They have a silicate skeleton with pores through which pseudopodia (false feet, not seen) of protoplasm project. As the animal floats in ocean currents the pseudopodia trap food particles on which the radiolarian feeds. Magnification: x150 when printed 10 centimetres wide.