Phylum Gnathostomulida Ax, 1956 - gnathostomulids
   Order Bursovaginoidea Sterrer, 1972
     Suborder Scleroperalia Sterrer, 1972
       1 Family Agnathiellidae Sterrer, 1972
       2 Family Clausognathiidae Sterrer, 1992
       3 Family Mesognathariidae Sterrer, 1972
       4 Family Gnathostomariidae Sterrer, 1972
       5 Family Rastrognathiidae R.M. Kristensen & A. Nørrevang, 1977
       6 Family Problognathidae (W. Sterrer & R.A. Farris, 1975) see Family Problognathiidae Sterrer & Farris, 1975
       7 Family Onychognathiidae Sterrer, 1972
       8 Family Gnathostomulidae Sterrer, 1972