Aquatic worms are called microdriles, and look like ordinary earthworms but they are generally smaller and thinner. They are found in and on the mud and sediment on the bottom of wetlands. Some species have gills and swim just above the substrate with body undulations. Other gill bearers live in tubes made of silt or mud with one end protruding into the water. Other species don’t have gills, and live in small burrows. Most aquatic worms feed on organic material such as diatoms (microscopic aquatic plants and animals), algal and plant material, as well as bacteria in silt. They feed by ingesting large amounts of mud and sediment, and digesting their food as it passes through. Aquatic worms are food for a wide range of animals, such as freshwater flathead, platypus and eels. Worms are generally very tolerant of water pollution, and may be found in large numbers in organically polluted rivers.