Micrometazoa more often found in activated sludge systems. They feed on bacteria, organic debris, small flagellates, ciliates and even other micrometazoa, and thereby clean the effluent lowering the turbidity. On the other hand rotifers are food for some worms. They are free lonely living microorganisms but some species may live in colonies or sessile. Its elongated and generally cylindrical body has cilia in the cephalic, that assist in food and transportation. Their presence is usually an indicator of good system efficiency due to it being associated with elevated sludge age and sludge in high oxidation stage.