http://www.collembola.org/key/isotidae.htm - Last updated on 2024.10.31 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

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; postantennal organ rim divided into 4 parts (fig.29)...................................... 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