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Radiolarian. Coloured scanning electron micrograph (SEM) of a radiolarian. Radiolarians are amoeboid protozoa that produce intricate mineral skeletons. They are found as zooplankton throughout the ocean, and their skeletal remains cover large portions of the ocean bottom as radiolarian ooze. Despite being single-celled protozoans Radiolaria are quite complex, sophisticated organisms. The body is divided into a central capsule which contains the endoplasm and nucleus (or nucleii) and the extracapsulum which contains peripheral cytoplasm composed of a frothy bubble-like envelope of alveoli and a corona of ray-like axopodia and rhizopodia. They feed on other zooplankton, phytoplankton and detritus using their axopodia and rhizopodial. Magnification: x700 at 10 centimetres wide. (KEYSTONE/SCIENCE PHOTO LIBRARY/STEVE GSCHMEISSNER/SCIENCE PHOTO LIBRARY)