An order of nematodes in which the amphids are simple spirals that appear as elongate loops, shepherd's crooks, question marks, or circular forms. The cephalic sensilla are often separated into three circlets: the first two are papilliform or the second coniform, and the third is usually setiform; rarely are the second and third whorls combined. Body annulation is simple. The stoma is anteriorly funnel shaped and posteriorly tubular; rarely is it armed. Usually the esophagus ends in a bulb that may be valved. In all but a few taxa the females have paired gonads. Male preanal supplements are generally tubular, rarely papilloid.