Key to the species of Tripylella

1. Tail with uniform tapering...............................................................................2

- Tail with abrupt tapering................................................................................4

2. Body length more than 1 mm; outer labial setae more than 7 µm................................................3

- Body length less than 1mm; outer labial setae less than 4 µm.......................................... T. minuscula

3. Body length 1810–1832 µm; outer labial setae 13–14 µm; caudal setae on tail present.......... Tripylella australis sp. nov.

- Body length 1080–1400 µm; outer labial setae 7–9 µm; caudal setae on tail absent......................... T. maiuscula

4. Subventral teeth absent; smooth cuticle............................................................. T. iucunda

- Subventral teeth present; annulated cuticle..................................................................5

5. Two large teeth in the posterior stomatal chamber and two subventral teeth in a smaller anterior chamber.......... T. dentata

- Stoma with one dorsal and two subventral teeth..............................................................6

6. Subventral teeth posterior to dorsal tooth........................................................ .. T. intermedia

- Subventral teeth anterior to dorsal tooth....................................................................7

7. Dorsal tooth large; excretory pore absent...................................................... T. subintermedia

- Dorsal tooth small; excretory pore present or absent..........................................................8

8. Excretory pore present.................................................................................9

- Excretory pore absent......................................................................... T. quitoensis

9. Body length 0.8–1.0 mm; caudal setae on tail absent................................................... T. muscusi

- Body length less than 0.8 mm, caudal setae on tail present....................................................10

10. Two pairs of caudal setae on tail; excretory pore 80–93 µm from anterior end.............................. T. mexicana

- Three pairs of caudal setae on tail; excretory pore 58–86 µm from anterior end........................... T. fatimaensis