Light micrograph of a freshwater cyclopoid Copepod with two egg sacks. Copepod crustaceans are generally small (0.5 to 2 mm) and they play an important role in various food chains, feeding on small algae or phytoplankton and being eaten by larger organisms such as fish. Microscopic contrast method : Darkfield. Magnification 50x when printed at 10 centimetres wide.