Key to the species of Oxyascaris (Cosmocercoidea)

1 - Gubernaculum present 2 Gubernaculum absent 4

2 - Males with an unpaired papillae at anterior cloacal lip 3 Unpaired papillae at anterior cloacal lip absent, male O. mcdiarmidi caudal papilla pattern distribution 5:0:6; spicules 612–689 μm in length, vulva post equatorial, cephalic vesicle present

3 - Cephalic vesicle absent, vulva pre equatorial, male caudal O. caatingae papilla pattern distribution 5:1:9 + 1; spicules 95–109 μm in length Vulva equatorial; male caudal papilla pattern distribution O. longum 9:0:6 + 1; spicules 232–258 μm in length

4 - Males with an unpaired papillae at the anterior cloacal lip 5 Unpaired papillae at anterior cloacal lip absent, cephalic O. oxyascaris vesicle present; lateral alae absent, male caudal papilla pattern distribution 4:0:3; spicules 150–206 μm in total length

5 - Males with 13 pairs of caudal papillae 6 Males with 7 pairs of caudal papillae, caudal papillae O. annulatum n. sp. pattern distribution 3:1:3 + 1, discreet lateral line only in females; spicules subequal, measuring right spicule 84–174 μm and left spicule 120–180 μm long

6 - Lateral alae well developed, excretory pore close to O. caudacutus isthmus-bulb region; male caudal papillae pattern distribution 6:0:7 + 1; spicules 122–134 μm in length; esophagus total length <630 μm in females Caudal papillae pattern distribution 6:0:7 + 1; spicules O. similis 160–193 μm in length; excretory pore in the middle portion of esophagus; esophagus total length ≥660 μm in females