Rotifers

Approximately 2,000 species of these microscopic invertebrates, common to freshwater habitats, occur worldwide. Rotifers were first discovered in the 1600s by Antoni van Leeuwenhoek, one of the first microscopists to study and describe microscopic organisms. Historically referred to as the Wheel Animalcule or Wheel Animal, rotifers were named for the shimmering rings of tiny beating cilia that draw food into their mouths.