They are elongated and cylindrical worms with generally tapered ends, with no trace of segmentation throughout the body. Move through rapid contractions of the body in the shape of "S" and are usually colorless, inhabiting the bottom sludge. They feed of particulate material and micro-organisms such as protozoa, other nematodes, rotifers and tardigrades. Are seen more often in biological contactors and aerated biofilters, where the flakes stick, leaving visible holes, are resistant to extreme temperatures and lower dissolved oxygen concentrations. They may indicate mixture of considerable concentration of sewage with industrial effluent. In activated sludge systems they rarely appear, indicating tendency to high sludge age.