Coloured scanning electron micrograph (SEM) of a Xiphostylus sp. radiolarian. 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: x500 when printed at 15 centimetres wide.