http://www.collembola.org/key/isotidae.htm - Last updated on 2017.02.28 by Frans Janssens
Checklist of the Collembola: Key to the genera of Isotomidae

This key is still under construction. Note that missing figures will be provided as soon as possible. Currently, the key is in the feasibility study phase to find out how to integrate in the checklist in a modular way a key that has been generated with DELTA.

Rationale

Check the rationale for taxa used and not used as well as subtaxonomic classification for some taxa.

Key

Note that no distinction between subtaxa and taxa is made in the key.

   
1(0).     Dorsal surface of abdominal segments 5 & 6 with a peculiar
            crown like median projection (fig.1)......................
             ........................................ Proctostephanus 26
          Dorsal surface of abdominal segments 5 & 6 without a
            peculiar crown like median projection................... 2
 

Fig.1.
 
2(1).     Males (fig.2c) with many peculiar heavy short spines or
            feather like setae (fig.2a&b)........................... 3
          Males without many peculiar heavy short spines or feather
            like setae or females only (fig.2c)..................... 5
 

Fig.2.
 
3(2).     Fourth abdominal segment with large lateral spines (fig.3)..
             .............................................. Guthriella 1
          Fourth abdominal segment without large lateral spines..... 4
 

Fig.3.
 
4(3).     Dens cylindrical (fig.4a); manubrium ventrally with 1 pair
            of setae..................................... Dimorphotoma
          Dens tapered to end (fig.4b); manubrium ventrally with many
            setae.......................................... Vertagopus 2
 

Fig.4.
 
5(2).     Posterior 2 segments of abdomen with at least some clear
            paired spines (fig.5)................................... 6
          Posterior 2 segments of abdomen without paired spines.... 26
 

Fig.5.
 
6(5).     Furcula reduced or absent, not reaching ventral tube
            (fig.5b-c).............................................. 7
          Furcula well developed, reaching ventral tube when at rest
            (fig.5a)............................................... 22
 
7(6).     Abdominal segments 4 & 5 fused (fig.6)...... Pseudofolsomia
          Abdominal segments 4 & 5 separate......................... 8
 

Fig.6.
 
8(7).     Eyes and pigment absent................................... 9
          Eyes and pigment present................................. 11
 
9(8).     Furcula absent........................................... 10
          Furcula present.................................. Isotomodes
 
10(9).    Anal spines 2 (fig.7a)......................... Martynovella
          Anal spines 4 (fig.7b)............................ Yosiiella
 

Fig.7.
 
11(8).    Ventral setae absent on manubrium........................ 12
          Ventral setae present on manubrium....................... 21
 
12(11).   Anal spines 2 - 3........................................ 13
          Anal spines 4 or more.................................... 14
 
13(12).   Cuticle reticulate (fig.8); unguiculus present..............
             ........................................... Sahacanthella
          Cuticle smooth; unguiculus absent.................... Uzelia
 

Fig.8.
 
14(12).   Anal spines 8............................................ 15
          Anal spines fewer than 8................................. 16
 
15(14).   Furcula absent................................ Tiancanthella
          Furcula present.............................. Octodontophora
 
16(14).   Anal spines 4............................................ 17
          Anal spines 5 or 6....................................... 19
 
17(16).   Fourth antennal segment with apical bulb (fig.9)............
             ......................................... Sibiracanthella
          Fourth antennal segment without apical bulb.............. 18
 

Fig.9.
 
18(17).   Cuticle more or less reticulate (fig.10)...... Tetracanthella
          Cuticle smooth, except for a few scattered spots.... Blissia
 

Fig.10.
 
19(16).   Anal spines 5 (fig.11b).................................. 20
          Anal spines 6 (fig.11a)..................... Gressittacantha
 

Fig.11.
 
20(19).   Anal spines 2 on segment 5 and 3 on segment 6 (fig.7b)......
             ................................................... Tuvia
          Anal spines 4 on segment 5 and one on 6 (fig.11b)...........
             .......................................... Pentacanthella
 
21(11).   Anal spines in two rows of 4 (fig.12).......... Weberacantha
          Anal spines varied but never in two rows of 4...............
             ........................................... Appendisotoma 3
 

Fig.12.
 
22(6).    Spines arranged on dorsal surface of fifth and/or sixth
            abdominal segments (fig.13a&b)......................... 23
          Spines terminal (fig.13c)...................... Hydroisotoma
 

Fig.13.
 
23(22).   Head of maxillae long and thin with slender lamellae
            (fig.14)..................................... Gnathisotoma 4
          Head of maxillae quadrate or reduced..................... 24
 

Fig.14.
 
24(23).   Ventral manubrial setae 10 or more....................... 25
          Ventral manubrial setae 4 or fewer............ Appendisotoma
 
25(24).   Cylindrical rugose or finely ciliate setae absent;
            multilaterally ciliate setae absent; thoracic spines
            absent............................................ Desoria 4
          Cylindrical rugose or finely ciliate setae present;
            multilaterally ciliate setae present; thoracic spines
            present..................................... Protodesoria 30
 
26(5).    Fourth & fifth segments distinctly separate, if the
            separation is indistinct then the non setaceous band
            separating them is the same width as those between other
            segments............................................... 27
          Fourth & fifth segments dorsally fused with sixth abdominal
            segment, often with a non-setaceous band between segments
            4 & 5, where this occurs the band is narrower than that
            between other segments. (fig.6)...................... 109
 
27(26).   Manubrium long, several times longer than dens and mucro....
             ............................................ Mucracanthus
          Manubrium often shorter than dens and mucro, if longer never
            more than 2 times as long.............................. 28
 
28(27).   Furcula absent........................................... 29
          Furcula present but sometimes rudimentary................ 33
 
29(28).   Fifth abdominal segment strongly reduced with 10 or fewer
            normal setae (fig.15)..................... Micranurophorus
          Fifth abdominal segment with many normal setae........... 30
 

Fig.15.
 
30(29).   Apical retractile bulb absent; eyes 0 - 5 + 5............ 31
          Apical retractile bulb present on fourth antennal segment
            (fig.16); eyes 2 + 2 - 8 + 8.................. Anurophorus
 

Fig.16.
 
31(30).   Abdominal segments 5 & 6 fused (fig.17a)................. 32
          Abdominal segments 5 & 6 separate (fig.17b).................
             ........................................ Pseudanurophorus
 

Fig.17.
 
32(31).   Tibiotarsus with clavate seta (fig.18)....... Antarctophorus
          Tibiotarsus without clavate setae................. Jesenikia
 

Fig.18.
 
33(28).   Furcula in the form of two mounds; tenaculum absent
            (fig.19)................................... Paranurophorus 5
          Furcula usually not so reduced; tenaculum present even if
            furcula reduced........................................ 34
 

Fig.19.
 
34(33).   Furcula reduced; manubrium without ventral setae; mucro if
            present fused to dens and falcate...................... 35
          Furcula varying in length; manubrium usually with ventral
            setae; mucro usually separate from dens, if fused, dens is
            elongate or mucro bidentate............................ 37
 
35(34).   Cuticle coarsely granulate (fig.20)............. Coloburella
          Cuticle smooth, sometimes mosaic, but never granulate.... 36
 

Fig.20.
 
36(35).   Apical bulb absent on fourth antennal segment.. Stachanorema
          Apical bulb present on fourth antennal segment (fig.21).....
             .......................................... Neocryptopygus
 

Fig.21.
 
37(34).   Postantennal organ absent and eyes absent....... Isotomiella
          Postantennal organ and/or eyes present................... 38
 
38(37).   Antennae straight; head narrower than or subequal to 2nd
            thoracic segment; mandibles symmetrical with typical molar
            plate (fig.22b)........................................ 39
          Antennae thin slightly bent towards each other and shorter
            than head (fig.22c); head broader than 2nd thoracic
            segment; mandibles asymmetrical, molar plate modified.
            (fig.22a)...................................... Metisotoma
 

Fig.22.
 
39(38).   Sixth abdominal segment not significantly longer than fifth,
            which has usually several rows of setae................ 40
          Sixth abdominal segment significantly longer than fifth,
            which has only one row of setae on the dorsal surface
            (fig.23)...................................... Secotomodes
 

Fig.23.
 
40(39).   Chaetotaxy of fifth and sixth abdominal segments not
            strikingly different, if macrochaetae present there are
            numerous small setae................................... 41
          Chaetotaxy of fifth and sixth abdominal segments strikingly
            different from fourth in chaetotaxy, both or sometimes
            only the sixth segment have strong straight macrochaetae
            and a few normal setae (fig.24)................ Isotomodes
 

Fig.24.
 
41(40).   Manubrium ventrally with 10 28 - usually 6 - or fewer
            setae and/or spines (fig.25a&b)........................ 42
          Manubrium ventrally with 11 - usually 14 - or more setae
            and/or spines (fig.25c&d).............................. 71
 

Fig.25.
 
42(41).   Body with slender truncate multilaterally ciliate setae;
            mucro 10% or less as long as dens.......... Villusisotoma 30
          Body without slender truncate, multilaterally ciliate setae;
            mucro more than 10% as long as dens.................... 43
 
43(42).   Cuticle granulate; dorsal surface of dens granulate but
            without knobs or annulations; mucro without setae, often
            with lamellae (fig.26)................................. 44
          Cuticle not granulate; dorsal surface of dens smooth
            annulate or with large knobs; mucro may be setaceous
            (fig.27)............................................... 47
 

Fig.26.
 

Fig.27.
 
44(43).   Dens with ventral setae.................................. 45
          Dens without ventral setae........................ Bonetrura
 
45(44).   Body with large ciliate blunt macrochaetae (fig.28).........
             ................................................ Jestella
          Body without large ciliate blunt macrochaetae............ 46
 

Fig.28.
 
46(45).   Dentes long and slender; dorsum of dentes with small
            triangular projections; dorsum of dentes with few setae;
            integument granulate....................... Propachyotoma 30
          Dentes not long and slender; dorsum of dentes without small
            triangular projections; dorsum of dentes with many setae;
            integument not granulate...................... Pachyotoma 15
 
47(43).   Manubrium with 2 or more ventral setae and/or spines..... 48
          Manubrium without ventral setae and/or spines............ 61
 
48(47).   Fifth and sixth abdominal segments with 13 long straight,
            blunt setae (fig.29); postantennal organ rim divided into
            4 parts....................................... Micrisotoma
          Fifth and sixth abdominal segments with normal setae;
            postantennal organ with simple rim..................... 49
 

Fig.29.
 
49(48).   Mucro with lateral setae and lamellae (fig.30).. Granisotoma
          Mucro without setae, lamellae present or absent.......... 50
 

Fig.30.
 
50(49).   Mucro dentate............................................ 51
          Mucro falcate (fig.31)................................... 60
 

Fig.31.
 
51(50).   Eyes 1 + 1 and mucro with 4 teeth and apical tooth much
            smaller than other teeth................. Antarcticinella 16
          Eyes not 1 + 1 or if 1 + 1 mucro with 2 or more teeth or
            with normal sized apical tooth......................... 52
 
52(51).   Dorsal heavy spines absent or present on both sexes...... 53
          Dorsal heavy spines numerous on body of males only (fig.32).
             ........................................... Dimorphotoma 23
 

Fig.32.
 
53(52).   Fourth antennal segment with "glands" at the base of most
            setae (fig.33)......................................... 54
          Fourth antennal segment without such glands.............. 55
 

Fig.33.
 
54(53).   Dens much longer than manubrium.................. Isotomedia
          Dens subequal to or slightly longer than manubrium..........
             ........................................... Womersleyella
 
55(53).   Abdominal segments 5 & 6 fused........................... 56
          Abdominal segments 5 & 6 separated............... Proisotoma
 
56(55).   Manubrium longer than dens (fig.34a)............... Dagamaea
          Manubrium shorter than dens (fig.34b).................... 57
 

Fig.34.
 
57(56).   Mucro with 3-5 teeth..................................... 58
          Mucro with two teeth..................................... 59
 
58(57).   End of dens usually with clear appendage (fig.35); ommatidia
            present..................................... Appendisotoma 3
          End of dens without appendage; ommatidia absent.. Mucrosomia
 

Fig.35.
 
59(57).   Manubrium with 10 ventral manubrial setae...... Isotominella
          Manubrium with 2-6 ventral manubrial setae..................
             ............................................ Cryptopygus 29
 
60(50).   Dens with a single pair of ventral setae......... Mucrotoma 29
          Dens with more than a single pair of ventral setae.... Arlea
 
61(47).   Dens often annulate or knobbed; mucro different.......... 62
          Dens smooth and cylindrical; mucro unique (fig.36), often
            with setae.................................... Archisotoma
 

Fig.36.
 
62(61).   Eyes absent, pigment absent, furcula very short, fifth and
            sixth abdominal segments normal (fig.37a).... Isotomodella
          Eyes present, if eyes are 2 + 2 or fewer then fifth and
            sixth abdominal segments are elongate or the furcula
            normal (fig.37b)....................................... 63
 

Fig.37.
 
63(62).   Sixth abdominal segment with a group of long straight setae
            projecting posteriorly (fig.38)................... Narynia
          Sixth abdominal segment without a group of long straight
            setae projecting posteriorly........................... 64
 

Fig.38.
 
64(63).   Dens ventrally with more than 1 + 1 setae (fig.39c)...... 65
          Dens ventrally with no more than 1 + 1 and dorsally with 1-5
            setae (fig.39a&b)...................................... 68
 

Fig.39.
 
65(64).   Dentes not strongly tapered; mucro not much shorter than
            dens; antennae and legs without cylindrical blunt or
            truncate setae......................................... 66
          Dentes strongly tapered; mucro much shorter than dens;
            antennae and legs with cylindrical blunt or truncate
            setae........................................ Burmisotoma 30
 
66(65).   Dens annulate or with uneven anterior folds, knobs or large
            humps, each of which occupies on a part of the length of
            the dorsal surface..................................... 67
          Dens dorsally with smooth surface............... Ballistura 18
 
67(66).   Mucro with lamellae (fig.40a).................. Clavisotoma 17
          Mucro without lamellae (fig.40b)................. Proisotoma
 

Fig.40.
 
68(64).   Eyes 1 + 1 - 2 + 2............................... Folsomides
          Eyes 4 + 4 - 8 + 8....................................... 69
 
69(68).   Dens and mucro fused............................ Subisotoma 24
          Dens and mucro sharply separated......................... 70
 
70(69).   Tenent hairs clavate........................... Haploisotoma
          Tenent hairs not clavate or absent.............. Folsomides 31
 
71(41).   Dens clearly narrowed distally, if weakly narrowed then
            dorsally crenulate or knobbed, dorsal and ventral surfaces
            of dens clearly distinguished by the number and thickness
            of their setae......................................... 72
          Dens cylindrical, not narrowed distally, normally
            multilaterally setaceous (fig.41)............ Hydroisotoma
 

Fig.41.
 
72(71).   Dens with spines (fig.42)................................ 73
          Dens without spines...................................... 79
 

Fig.42.
 
73(72).   Abdominal segments 2 - 4 with bothriotricha (fig.43)..... 74
          Abdominal segments 2 - 4 without bothriotricha........... 75
 

Fig.43.
 
74(73).   Dental spines serrate (fig.44b)................ Acanthomurus
          Dental spines simple (fig.44a)................... Tomocerura
 

Fig.44.
 
75(73).   Dental spines in up to 4 rows all of one type............ 76
          Dental spines of 2 types, 1 slender and a second short and
            stout (fig.45)................................ Spinocerura
 

Fig.45.
 
76(75).   Manubrium with spines (fig.46)........................... 77
          Manubrium without spines................................. 78
 

Fig.46.
 
77(76).   Dental spines in single row.................... Folsomotoma 14
          Dental spines in two rows........................ Semicerura
 
78(76).   Mucro with large apical tooth and 2 clear lamellae
            (fig.47a)...................................... Tibiolatra
          Mucro with small or no apical tooth and only 1 clear lamella
            (fig.47b)...................................... Setocerura
 

Fig.47.
 
79(72).   Body with scale like setae (fig.48)......... Araucanocyrtus 25
          Body without scale like setae............................ 80
 

Fig.48.
 
80(79).   Abdominal segments 2 - 4 with bothriotricha (fig.49)..... 81
          Abdominal segments 2 - 4 without bothriotricha........... 84
 

Fig.49.
 
81(80).   The anterior third antennal segment organ normal,
            bothriotricha ciliate.................................. 82
          The anterior third antennal segment organ with 10 or more
            thickened sensillae (fig.50).................... Axelsonia
 

Fig.50.
 
82(81).   Dens ventrally with coarsely unilaterally serrate setae
            (fig.51)..................................... Acanthomurus
          Dens ventrally without coarsely unilaterally serrate setae..
             ...................................................... 83
 

Fig.51.
 
83(82).   Mucro 3 toothed................................ Psammisotoma
          Mucro 4 or 5 toothed............................. Isotomurus
 
84(80).   Dorsal surface of dens annulate or smooth (fig.52c&d).... 85
          Dorsal surface of dens knobbed (fig.52a&b).............. 108
 

Fig.52.
 
85(84).   Tibiotarsus with clavate setae (fig.53a)................. 86
          Tibiotarsus without clavate setae (fig.53b).............. 90
 

Fig.53.
 
86(85).   Claw with clear pseudonychia (fig.54a)........ Pteronychella
          Claw without pseudonychia (fig.54b)...................... 87
 

Fig.54.
 
87(86).   Mucro 3 toothed or with extremely minute apical fourth
            toothlet............................................... 88
          Mucro 4 toothed.................................. Vertagopus 7
 
88(87).   Abdominal segments 5 & 6 fused (fig.55a). Pseudisotoma 8
          Abdominal segments 5 & 6 separate (fig.55b).............. 89
 

Fig.55.
 
89(88).   Manubrium and/or body with papillate or strongly glandular
            setae (fig.56)................................. Procerura 22
          Manubrium and/or body without papillate or strongly
            glandular setae............................. Womersleyella
 

Fig.56.
 
90(85).   Mucro falcate......................................... Arlea
          Mucro with 2 or more clear teeth......................... 91
 
91(90).   Head of maxillae long and thin with slender lamellae; setae
            on anterior surface of ventral tube absent. (fig.57a).....
             ............................................ Gnathisotoma
          Head of maxillae quadrate or reduced; setae on anterior
            surface of ventral tube present (fig.57b&c)............ 92
 

Fig.57.
 
92(91).   Claws normal............................................. 93
          Claws unique (fig.58)............................ Cheirotoma 9
 

Fig.58.
 
93(92).   Lateral teeth of unguis enlarged forming tooth like
            pseudonychia (fig.54a)...................... Pteronychella 6
          Lateral teeth of unguis small, even if large not forming
            pseudonychia........................................... 94
 
94(93).   Mucro minute less than 0. 008 mm in length, weakly bidentate
            or falcate.................................. Protoisotoma 30
          Mucro not minute, with three or more teeth............... 95
 
95(94).   Anterior two eyes arranged together with others in one patch
            (fig.59), if eyes present; postantennal organ clear.... 96
          Anterior two eyes far from others, viewing forward;
            postantennal organ obscure......................... Myopia
 

Fig.59.
 
96(95).   Ventromedial group of manubrial setae normal (fig.60c&d). 97
          Ventromedial group of manubrial setae spine like
            (fig.60a&b)........................................... 107
 

Fig.60.
 
97(96).   Eyes 0 + 0 - 5 + 5 if present in a squarish eye spot
            (fig.61b).............................................. 98
          Eyes 6 + 6 - 8 + 8 in long eyespot (fig.61a)............ 103
 

Fig.61.
 
98(97).   Tibiotarsus bearing feathered setae (fig.62)................
             ............................................. Marisotoma 10
          Tibiotarsus not bearing feathered setae.................. 99
 

Fig.62.
 
99(98).   Last abdominal segments with many small sensory setae
            (fig.63)..................................... Sericeotoma 21
          Last abdominal segments with very few or no small abdominal
            sensory setae......................................... 100
 

Fig.63.
 
100(99).  Median distal setae on venter of manubrium absent
            (fig.64a)...................................... Azoritoma
          Median setae present on venter of manubrium (fig.64b).. 101
 

Fig.64.
 
101(100). Mucro quadridentate (fig.65b)................ Misturasotoma
          Mucro tridentate (fig.65a)............................. 102
 

Fig.65.
 
102(101). Fifth and sixth abdomional segments fused.... Pseudosorensia
          Fifth and sixth first abdominal segmentominal segments
            separate...................................... Parisotoma 11
 
103(97).  Postantennal organ located less than 2 times the diameter of
            the nearest eye distant from same..................... 104
          Postantennal organ located more than 2. 5 times the diameter
            of nearest eye distant from same............... Paracerura
 
104(103). Abdomen with peculiar dorsal, terminal, dental swelling
            (fig.66)........................................... Aackia
          Abdomen without peculiar dorsal, terminal, dental swelling..
             ..................................................... 105
 

Fig.66.
 
105(104). Inner apex of 1st and 2nd antennal segments with projecting
            sharp angles (fig.67)......................... Halisotoma 12
          Inner apex of 1st and 2nd antennal segments without
            projecting sharp angles............................... 106
 

Fig.67.
 
106(105). Manubrium and/or body with papillate or strongly glandular
            setae (fig.56)................................. Procerura 27
          Manubrium and/or body without papillate or strongly
            glandular setae.................................. Desoria 13
 
107(96).  Eyes 4 + 4 or fewer............................ Folsomotoma 14
          Eyes 6 + 6 - 8 + 8.................................. Isotoma
 
108(84).  Dens subapically with a long strong seta (fig.27)... Agrenia
          Dens subapically without strong seta............ Panchaetoma
 
109(26).  Mucro falcate (fig.31) or toothed; postantennal organ
            absent.......................................... Folsomina
          Mucro toothed; postantennal organ present............... 110
 
110(109). Mandible with apical teeth; maxilla with normal distal
            ciliations (fig.68b).................................. 111
          Mandible without apical teeth; maxilla without normal distal
            ciliations (fig.68a)....................... Gnathofolsomia
 

Fig.68.
 
111(110). Dentes with a strong internal spine (fig.69).. Pectenisotoma
          Dentes without strong internal spine............... Folsomia

Fig.69.
 


Endnotes

1 Only muskegis will key out here. The placement of other species usually considered in this subgenus is in doubt.

2 Ecomorphic males.

3 Proisotoma (Appendisotoma).

4 Ecomorphic form.

5 Coloburella (Paranurophorus).

6 Some species of Desoria (viz. subaequalis) may key out here.

7 Desoria nivea winter form may key out here.

8 Isotoma (Pseudisotoma).

9 Isotoma (Cheirotoma).

10 Isotoma (Marisotoma).

11 Isotoma (Parisotoma). Pseudosorensia runs here, but is doubtfully separable from Parisotoma.

12 Isotoma (Halisotoma).

13 Isotoma (Desoria).

14 Isotoma (Folsomotoma).

15 Proisotoma (Pachyotoma).

16 This is a very questionable separation. It assumes that no species of Proisotoma s. str. has this combination of features.

17 Proisotoma (Clavisotoma). Potapov (2001) points out that this genus at present is best considered as a synonym of Ballistura.

18 Proisotoma (Ballistura).

19 The present state of taxonomy in the subgenera of Proisotoma is such that clear separations are not possible.

20 Folsomides (Subisotoma).

21 Isotoma (Sericeotoma).

22 We have examined types of Papillomurus fuscus, ochaceus, dissimilis and Procerura fasciata serrata, violacea and purpurea. Procerura purpurea and violacea as well as ochraceus would key out to Papillomurus as as defined above. They not only have papillate setae on the manubrium but most body setae have glandular bases. They also lack dental spines. The Holotypes of serrata and fasciata are immature and their position remains in doubt. The 4 species with adults also share a peculiar feature of having smooth bothriotricha - like setae on the Fifth but not 3rd or 4th abdominal segments. Until others of Salmon's genera have been re-examined we do not feel safe in using this characteristic. Thus Papillomorus and Procerura must be considered synonyms. The name Procerura has page priority over Papillomurus.

23 Females only.

24 Proisotoma (Subisotoma).

25 This genus falls between the families Paronellidae and Isotomidae. It has chaetotaxy, body form, lack of PAO and scale like setae as do members of Paronellidae. On the other hand it has a tapering dens, and no trochanteral organ as members of the Isotomidae.

26 The females of Dimorphotoma porcella may key out here.

27 Most of the species of Procerura would key out to Desoria. They either have such weakly clavate tenent hairs or acuminate ones that nobody would key them as Procerura.

28 If specimens have 10 ventral setae it is best to run them out both ways since subadult specimens of some species with more than 11 setae as adults have only 10 such setae.

29 Some species of Proisotoma will key out here.

30 Extinct genus.

31 The species of Folsomides that have 5 + 5 or 6 + 6 ocelli will key out here.



References