Rotifers, also called wheel animalcules, are microscopic animals already discovered by Antony van Leeuwenhoek in 1703. They are one of the smallest animals on earth.
Rotifers can be found in almost all freshwater environments, and occasionally in brackish and marine habitats. But they also live in the thin water films of moist soil, leaf litter, mosses, lichens and even on crustaceans and aquatic insect larvae.
Rotifers are small, transparent, multicellular animals having specialized organ systems, including a complete digestive system with mouth and anus. Most species are smaller than 1 millimeter and feed on bacteria, unicellular algae and dead organic material.