✯ Radiolarian, SEM, Coloured scanning electron micrograph (SEM) of the shell of a radiolarian. Radiolaria are single-celled protozoans that are found in marine plankton. This radiolarian has a spherical 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: x435 when printed 10 centimetres wide.✯
Diatoms are a major group of algae, and are one of the most common types of phytoplankton. Most diatoms are unicellular, although they can exist as colonies in the shape of filaments or ribbons (e.g. Fragillaria), fans (e.g. Meridion), zigzags (e.g. Tabellaria), or stellate colonies (e.g. Asterionella). Diatoms are producers within the food chain.