Bdelloidea /ˈdɛlɔɪdiə/ (Greek βδελλα, bdella, "leech-like") is a class of rotifers found in freshwater habitats all over the world. There are over 450 described species of bdelloid rotifers (or 'bdelloids'), distinguished from each other mainly on the basis of morphology. The main characteristics that distinguish bdelloids from related groups of rotifers are exclusively parthenogenetic reproduction and the ability to survive in dry, harsh environments by entering a state of desiccation-induced dormancy (anhydrobiosis) at any life stage. Bdelloid rotifers are microscopic organisms, typically between 150 and 700 µm in length. They are slightly too small to be seen with the naked eye, but appear as small white dots through even a weak hand lens.