Zooplankton (from Greek zoe = life, plankton = wanderer) are aquatic animals that cannot completely control their own movements against waves or currents of water. They are part of the group of organisms called plankton, which are drifters. Thus, zooplankton are the animal drifters. However, there are many varieties of zooplankton that have a limited ability to move. For example, many types of copepods, one of the dominant marine zooplankton, carry out vertical migrations each day. They move to the surface waters at night to feed, and return to deeper waters in the morning to avoid being eaten. Despite these limited movements, these organisms are considered zooplankton because they are still not strong enough to swim any great distance against the currents. While the great majority of zooplankton are microscopic, many can be seen with the naked eye. For example, jellyfish, which are clearly visible without a microscope, are zooplankton...