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Most animals that belong to the group of zooplankton are microscopically small, 0.01 to 0.16 inches long.
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Even though easily visible by naked eye, jelly fish is also classified as zooplankton because it cannot actively swim against the current.
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Most types of zooplankton have transparent body (which aids in camouflage). Species of zooplankton that live in fishless ponds have brightly-colored, usually orange or blue body.
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Most animals that belong to the group of zooplankton have long antennas on top of the head and elongated, cylindrical or torpedo-shaped body covered with protective shell. Some species are legless, while others have few pairs of leafy legs and flagella and cilia on the body.
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Name "zooplankton" originates from two Greek words: "zoon" which means "animal", and "planktos" which means "drifter". Name refers to the inability of these tiny animals to swim on their own.
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Adaptations such as flattened body, spines on the shell, low-density materials stored in the body, as well as movement of flagella and cilia prevent sinking of zooplankton.
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Zooplankton is dynamic community. Number of species and size of the population depend on the season.
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Zooplankton consists of temporary members such as larvae of fish and crabs which live as zooplankton only during the larval stage, and various species of protozoa, mollusks, echinoderm, arthropods...which spend their entire life as free-floating organisms.
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Zooplankton is mostly restricted to the upper parts of the water. Some species of animals spend day in deep water and migrate toward the surface at night.
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Diet of zooplankton is based on the algae and bacteria (phytoplankton) and tiny animals.
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Zooplankton is important source of food for fish, salamanders, aquatic insects and large marine animals such as whales.
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Some species of zooplankton inhabit ponds that dry periodically. They spend dry periods of year in the mud, hidden inside protective cases.
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Zooplankton reproduces quickly and rapidly increases population size. Under favorable conditions, population size can increase for 30% in 24 hours.
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Without environmental factors which keep reproduction of some species of zooplankton (such as Filinia) under control, entire world would be covered with 3-feet-thick layer of zooplankton in 130 days.
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Lifespan of zooplankton depends on the species. Daphnia, for example, can survive up to 30 days.
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