Bdelloid rotifer, light microscopy. Rotifers are microscopic aquatic animals that are related to roundworms. They have a ring of cilia around their mouth at the head end, which rhythmically beat creating a current to draw in bacteria, algae and other food. The majority of rotifers are found in fresh water. They are very common and widespread. Bdelloid rotifers are unusual in that they are all female and reproduce parthenogenetically. Filmed with differential interference contrast illumination.