Azygiida is an order of flatworms belonging to the class Rhabditophora. Families: * Accacoeliidae Odhner, 1911 * * Albulatrematidae * Aphanhysteridae * Areobiotrematidae * * Azygiidae Lühe, 1909 * Bathycotylidae Dollfus, 1932 * Bivesiculidae Yamaguti, 1934 * Botulidae * * Cylindrorchiidae * Dictysarcidae Skrjabin & Guschanskaja, 1955 * Didymozoidae Monticelli, 1888 * Halipegidae * Hemiuridae Looss, 1899 * Hirudinellidae Dollfus, 1932 * Isoparorchiidae Travassos, 1922 * * Mabiaramidae * * * Ptychogonimidae Dollfus, 1937 * * Sclerodistomidae Odhner, 1927 * Syncoeliidae Looss, 1899 * Tetrasteridae