Nemathelminthes Gegenbaur, 1859 see Phylum Nematoda Gegenbaur, 1859
   Class Nematoda Gegenbaur, 1859
     Subclass Secernentia (Von Linstow, 1905) Andrássy, 1976
       Order Rhabditida Chitwood, 1933
         Suborder Cephalobina Andrassy, 1974
           26 Family Cephalobidae Filipjev, 1934
           27 Family Osstellidae Heyns, 1962
           28 Family Panagrolaimidae Thorne, 1937
           29 Family Myolaimidae Andrássy, 1958
           30 Family Brevibuccidae Paramonov, 1956