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

Published as part of Serrano, Paula Carolina & Digiani, María Celina, 2016, First record of Viannaiidae (Nematoda: Trichostrongylina) in fossorial rodents (Ctenomys spp.) from Central Argentina, with description of a new genus and species, pp. 151-160 in Zootaxa 4168 (1) on page 157, DOI: 10.11646/zootaxa.4168.1.8, http://zenodo.org/record/261625