Torrenticolidae, Piersig, 1902

Gu, Xinyao, Jin, Daochao, Yi, Tianci & Guo, Jianjun, 2019, Contributions to the knowledge of Torrenticolid water mites (Acari: Hydrachnidia) in Doupengshan, China, Zootaxa 4695 (2), pp. 101-121 : 117-118

Key to the known species of the family Torrenticolidae in China. (modified to Gu et al. 2018, 2019)

1. Six pairs of acetabula.................................................................................. 2

- Three pairs of acetabula, the tip of Cx-I with a seta-like extension, P-2 and P-3 both with a feathered seta on the ventral sur- face............................................................. Testudacarus binodipalpis Guo & Jin, 2005

2. P-4 long, more than twice as long as W.................................................................... 3

- P-4 short, not more than twice as long as W, P-5 with broad, blunt terminal setae................................................................................................ Neoatractides proclusteroseta Gu & Guo, 2018

3. Gnathosoma dorsal apodeme short, P-2 and P-3 with obvious ventral prolongations or hyaline expansions............... 4

- Gnathosoma dorsal apodeme long, P-2 and P-3 without projections on ventral side................................ 17

4. Dorsal plate arrangements: 4+1.......................................................................... 5

- Dorsal plate arrangements: 2+1, P-3 distal margin with denticles, P-4 stocky............................................................................ Torrenticola taiwanicus Pešić, Semenchenko, Chatterjee, Yam, Chan, 2011

5. Infracapitular rostrum short (<1/2 of gnathosoma dL)................................................ 6

- Infracapitular rostrum long (≥1/2 of gnathosoma dL)........................................................ 10

6. Palp relatively thin and long............................................................................. 7

- Palp robust and compact, P-2 shorter than P-4, Cx-IV with a prominent suture line of starting at right angle from genital field, laterally curved anteriorly........................ T. nanshihensis Pešić, Semenchenko, Chatterjee, Yam, Chan, 2011

7. P-3 with a triangular, relatively short ventral projection....................................................... 8

- P-3 with a very long tapering ventral projection which is curved distally, larger than projection on P-2.............................................................................. T. projectura Pešić, Chatterjee, Yam, Chan, 2012

8. Infracapitular bay deep, ventral apodeme L about two times of dorsal apodeme.................................... 9

- Infracapitular bay shallow, ventral apodeme L three times longer than dorsal apodeme................. T. curta Jin, 1997

9. Idiosoma roundish, the lateral view of infracapitulum acute triangle-like................... T. siamis Pešić & Smit, 2009

- Idiosoma elliptical, the lateral view of infracapitulum regular triangle-like................ T. trigona Gu & Guo , sp. nov.

10. Ventral extensions of P-2 & P-3 with some teeth............................................................ 11

- Ventral extensions of P-2 & P-3 smooth.................................................................. 13

11. Infracapitular bay U-shaped............................................................................ 12

- Infracapitular bay V-shaped, posterior half of dorsal plate red......................... T. alargada Goldschmidt, 2007

12. Dorsal apodeme of infracapitulum with a fine spine, AP close to the line of primary sclerotization, E 4 at the same level as the 3 rd pair of acetabula.................................................................. T. yanjinensis Jin, 1997

- Dorsal apodeme of infracapitulum with a broad spine, AP on the line of primary sclerotization, E 4 at the same level as the 4 th pair of acetabula.................................................................... T. dentipalpis Jin, 1997

13. The concavity between the ventral prolongations of P-4 small................................................. 14

- The concavity between the ventral prolongations of P-4 big and obvious, and with four setae on the ventral prolongations, idiosoma oblate.............................................................. T. fodingensis Gu & Guo, 2018

14. Ap anterior to V 2. .................................................................................... 15

- Ap on the line with V 2. ................................................................................ 16

15. P-2 shorter than 1/3 palp L, idiosomal frontal margin with a convex outline................. T. nipponica ( Enami, 1940)

- P-2 longer than 1/3 palp L, ventral margin convex, ventrodistal protrusion bluntly pointed and slightly curved towards distal, gnathosoma elongated, chelicera long and straight................................ T. tenuichelicera Gu & Guo, 2018

16. The shape of gnathosoma elongated and compressed, idiosomal frontal margin with a flat outline, body pale yellow, Cx-II+III mL short......................................................................... T. semicolor Viets, 1977

- The posterior segment of gnathosoma conspicuous and towering, body pale tawny, Cx-II+III mL relatively long............................................................................................ T. tetrapora Viets, 1935

17. Idiosoma elongated, L/W ratio more than 1.5.............................................................. 18

- Idiosoma roundish or slightly oval, L/W ratio less than 1.5.................................................... 19

18. Idiosoma L/W ratio 1.6–1.9, frontal margin of idiosoma with a flat protrusion; E 4 posterior to Gf; gnathosoma dorsal apodeme pointed............................................ M. tuzovskyi Pešić, N. Kumar, K. Kumar & S. Kumar, 2006

- Idiosoma L/W ratio 1.5–1.6, E 4 at the same level as the posterior edge of Gf; gnathosoma dorsal apodeme with a blunt end............................................................................ M. xiaoxiensis Gu & Guo, 2019

19. Gnathosoma and palp normal, chelicera more or less curved.................................................. 20

- Gnathosoma relatively long and slender, palp comparatively short and stocky, chelicera straight. M. pinapalpis ( Cook, 1967)

20. P-2 and P-3 ventrodistal setae smooth.................................................................... 21

- P-2 and P-3 ventrodistal setae feathered.................................................................. 23

21. E 4 on the same line with the 4 th (male) or 5 th (female) pair of acetabula, Idiosoma roundish.......................... 22

- E 4 posterior to Gf, Idiosoma oval, D 2 anterior to the anterior edge of muscle scars, gnathosoma proportionally short and tapering gradually towards the distal end, P-4 much narrower................................... M. setivalvata ( Cook, 1967)

22. The tip of Cx-I sharp and with a long elongated cuticular extension.............. M. hamatapodemus Gu & Guo , sp. nov.

- The tip of Cx-I with a short and small cuticle extension............................. M. macrocorpis Gu & Guo, 2019

23. Infracapitular bay V-shaped, P-2 longer or shorter than P-4................................................... 24

- Infracapitular bay U-shaped, frontal margin of idiosoma distinctly concave, P-2 almost as long as P-4.................................................................................................. M. stadleri (Walter, 1924)

24. Gnathosoma rostrum short (1/5 of gnathosoma dL) and tapering abruptly towards the distal end, gnathosoma dorsal apodeme longer than ventral apodeme, and with a blunt end, frontal margin of idiosoma concave, P-2 shorter than P-4......................................................................................... M. oxystomus (K. Viets, 1935)

- Gnathosoma rostrum relatively long and gradually tapering towards the distal end, gnathosoma dorsal apodeme L equal in length with the ventral apodeme and with the ventral serrated teeth, Cx-I with seta-like cuticle extensions at the tip, dorsodistal seta on P-3 smooth and longer than P-4, P-2 longer than P-4................................ M. serratifera Jin, 1997