[Kingdom] Animalia Linnaeus, 1758 - animals
   Grade Enterozoa
     Grade Cœlomata
       Phylum Nematoidea
         [Class] Nematoidea Rudolphi, 1808 see Phylum Nematoda Gegenbaur, 1859
           [Family] Mermithidæ Weinland, 1858
             1 Genus Mermis Dujardin, 1842
             2 Genus Sphærularia Dufour, 1837