Key to the genera of Viannaiidae parasitic in caviomorphs

1 Bursa with right ray 8 hypertrophied, left ray 8 incorporated in left trunk of rays 2–6. Dorsal ray tripartite and arising from right ray 8. Parasites of Cuniculidae ............................................................. Oswaldonema

- Rays 8 and dorsal ray not as above........................................................................ 2

2 Bursa asymmetrical, with dorsal ray hypertrophied and displaced rightwards. Right lobe more developed than left one. Syn- lophe with gap only on left side, between ridges 1' and 2'. Parasites of Ctenomyidae .................. Ischilinema gen. n.

- Bursa subsymmetrical or slightly dissymmetrical, dorsal ray not displaced. Synlophe with gaps on both lateral sides, left gap between ridges 1 and 1'................................................................................. 3

3 Left rays 3–6 of bursa fused, with convergent extremities. Parasites of Caviidae, Hydrochoerinae ........ Hydrochoerisnema

- Rays of bursa not fused.................................................................................4

4 Dorsal lobe well developed. Spicules twisted. Female monodelphic. Parasites of Caviidae (Caviinae and Hydrochoerinae), Dasyproctidae, Chinchillidae ..................................................................... Viannella

- Dorsal lobe short. Spicules not twisted. Female didelphic or semi-monodelphic (posterior uterine branch atrophied). Parasites of Cuniculidae and Dasyproctidae .................................................................. Avellaria