Key to the Neotropical species of the genus Xenylla
1 Furca absent......................................................................................... 2
- Furca present........................................................................................ 4
2 Head with dorsal setae c1 and c2 present.................. X. atrata (Salmon, 1944) (New Zeland, Argentina, Venezuela)
- Head with dorsal setae c1 present and c2 absent............................................................. 3
3 Head with dorsal setae l1 and l3 subequal in length................................................................ X. subacauda Stebaeva & Potapov, 1994 in: Babenko, Chernova, Potapov & Stebaeva, 1994 (Russia, Poland, Mexico)
- Head with dorsal setae l1 shorter than l3................................................................................. X. acauda Gisin, 1947 (Switzerland, Austria, Spain, Great Britain, Poland, Russia, USA, Mexico, Venezuela)
4 Mucro absent.............. X. boerneri Axelson, 1905 (Russia, Ukraine, Lativia, Finland, Austria, Switzerland, England)
- Mucro present........................................................................................ 5
5 Mucro seprated from dens.............................................................................. 6
- Mucro fused to dens.................................................................................. 23
6 Head with 4+4 ocelli....................................................................................... X. yucatana Mills, 1938 (Solomon Islands, Mexico, Sudan, Jamaica, Porto Rico, Thailand, Gabon, Gambie, Singapour, Brasil, Ecuador, West Indies, Galapagos)
- Head with 5+5 ocelli.................................................................................. 7
7 Dens with one seta, retinaculum with 2+2 teeth.............................................................. 8
- Dens with two setae, retinaculum with 3+3 teeth............................................................. 9
8 Tibiotarsi with 0,1,1 tenent hairs respectively.................................... X. saludoi Izarra, 1970 (Argentina)
- Tibiotarsi with 2,2,2 tenent hairs respectively............................... X. canadensis Hammer, 1953 (Canada) *
9 Ant. IV with 4 thick sensilla............................................................................ 10
- Ant. IV with 5–6 thick sensilla.......................................................................... 19
10 Tibiotarsus of first leg with 1 clavate tenent hair............................................................ 11
- Tibiotarsus of first leg with 2 clavate tenent hairs........................................................... 13
11 Tibiotarsi with 1,2,2 tenent hairs respectively...................................................................... X. welchi Folsom, 1916 (USA, Solomon Islands, Sudan, Pakistan, Singapour, Taiwan, Jamaica, Hawaii, Brasil, South Australia, Argentina, Chile, Peru, West Indies, French Guiana, Cuba)
- Tibiotarsi with 1,1,1 tenent hairs respectively.............................................................. 12
12 Head with dorsal setae l1 and l3 subequal in length......................... X. portoricensis Gama, 1976 (Porto Rico)
- Head with dorsal seta l3 longer than l1........................................ X. bellingeri Gama, 1969 (Jamaica)
13 Claw without inner tooth............................................ X. hodori Neves & Mendonça, 2017 (Brasil)
- Claw with inner tooth present........................................................................... 14
14 Head with dorsal seta l1 longer than l3................................................................... 15
- Head with dorsal setae l1 and l3 subequal in length......................................................... 16
15 Abd. I–III with seta p5 present.............................................. X. fernandesi Gama, 1974 (Portugal)
- Abd. I–III with seta p5 absent.................................... X. manuelae Queiroz & Mendonça, 2016 (Brasil)
16 Head with dorsal seta c2 absent.............................................................................. X. mucronata Axelson, 1903 (Sweden, Austria, Germany, England, Ukraine, Russia, Siberia, Costa Rica, Peru, Australia)
- Head with dorsal seta c2 present........................................................................ 17
17 Th. II–III with seta p2 aligned with seta p1......................................................................................... X. humicola (Fabricius, 1780) (Greenland, Central America, West Indies, Chile, Mexico, Cuba)
- Th. II–III with seta p2 displaced......................................................................... 18
18 Tibiotarsus of legs I–III with 19,19,18 setae respectively.............................. X. gwiazdowiczi sp. nov. (Peru)
- Tibiotarsus of legs I–III with 17,17,16 setae respectively................. X. spinosissima Najt & Rubio, 1978 (Falkland)
19 Tibiotarsus of first leg with 1 clavate tenent hair............................................................ 20
- Tibiotarsus of first leg with 2 clavate tenent hairs........................................................... 22
20 Tibiotarsi with 1,2,2 tenent hairs respectively, head with dorsal seta l1 longer than l3............................................................................................... X. wandae Queiroz & Mendonça, 2016 (Brasil)
- Tibiotarsi with 1,1,1 tenent hairs respectively, head with dorsal setae l1 and l3 subequal in length..................... 21
21 Ant. IV with 5 thick sensilla, head with dorsal seta c1 present... X. raynalae Najt, Thibaud & Weiner, 1990 (French Guiana)
- Ant. IV with 6 thick sensilla, head with dorsal seta c1 absent................... X. nirae Gama & Oliveira, 1994 (Brasil)
22 Mucro with apical globe present, Abd. IV without setae m1................................................................................................. X. villiersi Thibaud, 1963 (Ivory Coast, Angola, Gambie, Martinique)
- Mucro without apical globe, Abd. IV with setae m1.................. X. capixaba Fernandes & Mendonça, 2010 (Brasil)
23 Dens with 2 setae.................................................................................... 24
- Dens with 1 seta..................................................................................... 29
24 Tibiotarsi with 1,1,1 tenent hairs respectively.............................................................. 25
- Tibiotarsi with 2,2,2 tenent hairs respectively.............................................................. 26
25 Retinaculum with 2+2 teeth.................................................. X. brasiliensis Gama, 1978 (Brasil)
- Retinaculum with 3+3 teeth.............................................. X. subbellingeri Gama, 1976 (Trinidad)
26 Ant. IV with 5 thick sensilla................................................... X. simberloffi Gama, 1974 (USA)
- Ant. IV with 4 thick sensilla............................................................................ 27
27 Head with dorsal setae l1 and l3 subequal in length......... X. jamaicensis Gama, 1969 (Jamaica, Guadalupe, Martinique)
- Head with dorsal seta l1 longer than l3................................................................... 28
28 Dorsal body s-chaetae longer than regular setae............. X. maritima Tullberg, 1869 (Scandinavia, Brasil, Venezuela)
- Dorsal body s-chaetae and regular setae subequal in size................................................................. X. grisea Axelson, 1900 (Finland, RSA, England, Saint Helen Island, Belgium, Hawaii, USA, Chile, Porto Rico)
29 Retinaculum with 3+3 teeth............................................................................ 30
- Retinaculum with 2+2 teeth............................................................................ 32
30 Head with dorsal seta c1 absent.................................. X. capitata Thibaud & Massoud, 1980 (Guadalupe)
- Head with dorsal seta c1 present........................................................................ 31
31 Body with scattered pigment, colour blue-grey. X. cavernarum Jackson, 1927 (Trinidad, Jamaica, Solmon Islands, Argentina)
- Body without pigment, only eyes pigmented................................. X. subcavernarum Gama, 1969 (Brasil)
32 Claw without inner tooth................................................... X. duchesnea Wray, 1958 (Mexico)
- Claw with inner tooth present........................................................................... 33
33 Anal spines setiform, straight and slender.................................... X. christianseni Gama, 1974 (Mexico)
- Anal spines short on papillae........................................................................... 34
34 Mucro without lamella.............................. X. proxima Denis, 1931 (USA, Costa Rica, Guadelupa, Mexico)
- Mucro with lamella................................................................................... 35
35 Head with dorsal seta l1 shorter than l3............................... X. tullbergi Börner, 1903 (Europe, Switzerland)
- Head with dorsal seta l1 longer than l3................................................................... 36
36 Head with dorsal seta c1 present, Abd. IV with setae m1............................... X. wilsoni Gama, 1974 (USA)
- Head with dorsal seta c1 absent, Abd. IV without setae m1................ X. uniseta Gama, 1963 (Dalmatie, Yugoslavia)