Rotifers feeding. Light microscope footage of four rotifers (Ptygura sp.) feeding. Rotifers are common multicellular organisms found in pond water and help form the base of the food chain. Ptygura sp. builds a tube from its own excrement and other detritus, from which the corona of beating hair-like cilia protrudes, creating a current that sweeps food into the mouth. Filmed with differential interference contrast illumination.