Polarised light micrograph of a copepod (subclass Copepoda). This microscopic aquatic crustacean is found in waters around the world. Copepods may either be free living or parasitic on other organisms. They are the main constituent of zooplankton and therefore are very important as food organisms for fish, whales and other crustaceans. Copepods feed on other microscopic animals and plants. Magnification: x93 when printed at 10 cm wide.