An order of nematodes in which the variable stoma may or may not be armed with a dorsal tooth which may or may not be opposed by subventral denticles. The variable amphids range from reniform-to-elongate loops to simple or multiple spirals. The cephalic sensilla are generally in three whorls; however, the second and third whorls may be combined. Distinguishing the order is the cephalic capsule or helmet and the conspicuous somatic annuli. In some groups anterior and posterior adhesion tubes are utilized in locomotion.