Rotifers are small invertebrates in the Phylum Rotifera.They range in size from 100 to 2500 microns, with approximately 2000 described species. Rotifers are found in aquatic and semi-aquatic habitats, but are predominantly freshwater inhabitants. Most species are free-living herbivores, bacteriovores or predators, and possess a ciliated, wheel-like organ for feeding and locomotion. Rotifers move by swimming or crawling. Some sessile species are permanently attached to freshwater plants.