http://www.collembola.org/key/isotomur.htm - Last updated on 2017.10.31 by Frans Janssens
Checklist of the Collembola: Key to the species of Isotomurus, partim Western Europe

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.

Antonio Carapelli, Department of Evolutionary Biology, University of Siena
F. Frati, Department of Evolutionary Biology, University of Siena
P.P. Fanciulli, Department of Evolutionary Biology, University of Siena
R. Dallai, Department of Evolutionary Biology, University of Siena
Arne Fjellberg, Mageroveien 168, N-3145 Tjome, Norway
Frans Janssens, Department of Biology, University of Antwerp, Antwerp, B-2020, Belgium

Rationale

The rationale for taxa used and not used as well as subtaxonomic classification for some taxa is to be provided.

Key

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

1(0).   Trunk colour concentrated in distinctive patterns........... 2
        Trunk colour distributed uniformly......................... 12
 
2(1).   Pigment pattern in irregular patches........................ 3
        Pigment pattern in regular bands............................ 5
 
3(2).   Pigmentation as irregular stripes on posterior part of third
          to fifth abdominal segments............................... 4
        Pigmentation as irregular symmetrical patches on tergites.....
           ................................................. maculatus
 
4(3).   Mesochaetae ciliate; body with darker ribbon-like patches of
          pigmentation on the margins of tergites; legs uniformly
          coloured like tergites; dentes are dorsally covered by many
          setae, each one inserted in a papilla-like cuticular
          structure; furca: retinaculum with 10-15 ordinary setae.....
           ................................................. aetnensis
        Mesochaetae smooth; body with thin violet drawings mostly
          present on last abdominal tergites; legs whitish; dentes
          dorsally with many short setae, which are longer on lateral
          margins; furca: retinaculum with 14 to 32 ordinary setae....
           ................................................. nebulosus
 
5(2).   Pigment pattern longitudinal................................ 6
        Pigment pattern transversal................................ 10
 
6(5).   Lateral flaps of ventral tube with 11 + 11 to 20 + 20 setae;
          longitudinal middorsal pattern very wide, about 1/3 width of
          tergites.......................................... alticolus
        Lateral flaps of ventral tube with 3 + 3 setae; longitudinal
          middorsal pattern less than 1/5 width of tergites and
          sometimes absent on the last abdominal tergites........... 7
 
7(6).   Longitudinal middorsal pattern continuous and very pronounced,
          sometimes absent on fifth and sixth abdominal segment..... 8
        Longitudinal middorsal pattern interrupted or fainter,
          especially on third abdominal segment, with net-like
          ornaments on lateral parts of each tergite................ 9
 
8(7).   Dorsolateral pigmentation absent or very limited. unifasciatus
        Dorsolateral pigmentation abundant brownish...................
           ........................................... pseudopalustris 1
 
9(7).   Abdominal setae all smooth; mucro without lateral seta;
          unguiculus with inner corner tooth................ palustris
        Abdominal setae some smooth and some weakly feathered having 3
          to 5 ciliae laterally near the base of the seta, especially
          abundant on third abdominal segment; mucro with lateral
          seta; unguiculus without inner tooth............... plumosus 2
 
10(5).  Pigmentation dark on all tergites of second thoracic segment
          to second abdominal segment, completely covered...... rabili
        Pigmentation dark only on anterior parts of tergites....... 11
 
11(10). Macrochaetae multilaterally ciliate; ordinary setae abundant;
          trichobothrial formula: 3 + 3 + 1; lateral flaps with 3 + 3
          setae; retinaculum with 12-16 ordinary setae.... ghibellinus
        Macrochaetae unilaterally slightly ciliate; ordinary setae
          reduced if compared with species of the palustris group;
          trichobothrial formula: 0 + 1 + 1; lateral flaps with 5 + 5
          setae; retinaculum with 2 ordinary setae........... gallicus
 
12(1).  Background colour dark brownish or black................... 13
        Background colour light greenish or yellowish.............. 15
 
13(12). Colour black...................................... hadriaticus
        Colour brownish............................................ 14
 
14(13). Accp1-5 + as1 and 4 on abdominal segment iv; accp1-5 + as1 on
          abdominal segment v; accp1 and accp2 equally long as other
          accp setae on abdominal segment v; postantennal organ/dca:
          0. 8-1; l/antennae: 3. 5-4. 0.................... cassagnaui
        Accp1-5 + as1, 2 and 4 on abdominal segment iv; accp1-5 +
          as1-2 on abdominal segment v; accp1 and accp2 longer than
          the other accp setae on abdominal segment v; postantennal
          organ/dca: 1. 5; l/antennae: 2. 2................. fucicolus
 
15(12). Collophore with 3 + 3 lateral setae; dens dorsally crenulate;
          mucronal seta absent............................... graminis
        Collophore with up to 20 + 20 lateral setae; dens dorsally
          tuberculate; mucronal seta present................. prasinus

Endnotes

1 This key does not apply to the population of I. unifasciatus from Siena, where specimens resemble those of I. pseudopalustris.

2 This feathering is usually visible only under great enlargement, and on preparations of the tergits cut off and made transparant under the influence of KOH (Stach, 1947:462).


Differential diagnoses

aetnensis
Relative length of antennal segments i:ii:iii:iv are as 60:102:108:120. Mesochaetae ciliate. Body with darker ribbon-like patches of pigmentation on the margins of tergites. Legs uniformly coloured like tergites. Dorsal chaetotaxy of manubrium is composed of several ordinary slightly ciliate setae, which are longer near the distal margin, ventral side of manubrium is completely covered by several microchaetae, with the exception of a median thin longitudinal stripe and it also bears 2 longer and ciliate microchaetae. Dentes ventrally with setae less abundant and limited to the anterior part. Dentes dorsally with two sensilla near the middle part of each dens. Dentes are dorsally covered by many setae, each one inserted in a papilla-like cuticular structure. Colouration: antennal segment iii slightly darker. Colouration: in some specimens there is a very slight longitudinal median band, not visible to the naked eye. Colouration: patch of pigmentation at the base of each antenna, or on the central part of the head. Furca: retinaculum with 10–15 ordinary setae. Habitus: body slender. Habitus: body length: 2–3 mm. Head: labium with 7 to 9 setae on each part of submentum. Head: postantennal organ elongated. Head: postantennal organ/dca: 0. 6. Irregular stripes dark brown. L/antennae: 2. 3. Legs: third tibiotarsus with 4 multilaterally ciliate macrochaetae. Pigment pattern in irregular patches. Pigmentation as irregular stripes on posterior part of third to fifth abdominal segments. Submentum with 7 + 7 to 9 + 9 setae. Tibiotarsal macrochaetae ciliate. Trunk colour concentrated in distinctive patterns.

alticolus
Lateral flaps of ventral tube with 11 + 11 to 20 + 20 setae. Longitudinal middorsal pattern very wide, about 1/3 width of tergites. Pigment pattern longitudinal. Pigment pattern in regular bands. Trunk colour concentrated in distinctive patterns.

cassagnaui
Accp1–5 + as1 and 4 on abdominal segment iv. Accp1–5 + as1 on abdominal segment v. Accp1 and accp2 equally long as other accp setae on abdominal segment v. Antennae violet. Body size reduced. Body length: 1. 2–1. 4 mm. Postantennal organ large if compared with the average of the genus. Habitus: habitus of isotoma 40a habitus: habitus of isotoma. Postantennal organ/dca: 0. 8–1. Background colour dark brownish or black. Colour brownish. L/antennae: 3. 5–4. 0. Legs: empodial appendage generally without tooth. Submentum with 4 + 4 to 6 + 6 setae. Trunk colour distributed uniformly.

fucicolus
Accp1–5 + as1, 2 and 4 on abdominal segment iv. Accp1–5 + as1–2 on abdominal segment v. Accp1 and accp2 longer than the other accp setae on abdominal segment v. Antennae not violet. Body slender. Body length: 1. 5–2 mm. Postantennal organ elongated. Habitus: habitus of isotoma 40b habitus: habitus of isotoma. Postantennal organ/dca: 1. 5. Background colour dark brownish or black. Colour brownish. L/antennae: 2. 2. Legs: empodial appendage without tooth. Submentum with 5 + 5 to 8 + 8 setae. Trunk colour distributed uniformly.

gallicus
Length of antennal segments i:ii:iii:iv are as 45:70:80:98. As1 and 4 + accp1–5 on abdominal segment iv. As1 + accp1–5 on abdominal segment v. Macrochaetae unilaterally slightly ciliate. Ordinary setae reduced if compared with species of the palustris group. Trichobothrial formula: 0 + 1 + 1. Lateral flaps with 5 + 5 setae. Anterior part of tergites with transverse dark band more or less diffuse on the rest of segment. Dorsal side of manubrium covered with several smooth setae mainly distributed on the anteromedian part and on the distal margin. Dental chaetotaxy made of several smooth microchaetae on the dorsal side and of very few ones on the ventral side. Retinaculum with 2 ordinary setae. Furca: mucro short 110b furca: mucro short. Furca: ventrally with numerous short setae, which are absent only in a narrow longitudinal stripe. Habitus: body thin. Habitus: body length: 1. 3–1. 4 mm. Habitus: body short 110b habitus: body short. Head: labium with 5 to 7 setae on each part of submentum. Head: postantennal organ very large if compared with other species of the genus. Head: postantennal organ/dca: 1. 6. L/antennae: 3. 24–3. 27. Legs: claw with lateral teeth. Legs: empodial appendage with or without tooth. Legs: third tibiotarsus with short ordinary setae and with at least 3 smooth macrochaetae. Pigment pattern transversal. Pigment pattern in regular bands. Pigmentation dark only on anterior parts of tergites. Submentum with 5 + 5 to 7 + 7 setae. Trunk colour concentrated in distinctive patterns.

ghibellinus
Length of antennal segments i:ii:iii:iv are as 45:60:72:80. As1, 2 and 4 + accp1–5 on abdominal segment iv. As1–2 + accp1–5 on abdominal segment v. Macrochaetae multilaterally ciliate. Ordinary setae abundant. Trichobothrial formula: 3 + 3 + 1. Lateral flaps with 3 + 3 setae. Anterior part of each tergite with a dark transverse band more or less diffuse on rest of segment, variability was observed in the thickness of the band some specimens are depigmented or entirely dark. Manubrium with several short setae and two dorsal macrochaetae on each side. Dentes with many ordinary setae on the ventral side, inserted in a circular area of the cuticle, dorsal chaetotaxy reduced and composed of short setae, mostly dispersed on the proximal side of dens. Retinaculum with 12–16 ordinary setae. Furca: ventrally with shorter setae densely present on central and distal margins. Habitus: body length: 2–3 mm. Head: labium with 6 to 10 setae on each part of submentum. Head: postantennal organ of regular shape. Head: postantennal organ/dca: 1. L/antennae: 2. 28. Legs: claw with inner teeth. Legs: empodial appendage frequently armed with a little tooth. Legs: third tibiotarsus with 4–5 ciliate macrochaetae, armed with a little tooth. Pigment pattern transversal. Pigment pattern in regular bands. Pigmentation dark only on anterior parts of tergites. Submentum with 6 + 6 to 10 + 10 setae. Trunk colour concentrated in distinctive patterns.

graminis
Background colour light greenish or yellowish. Collophore with 3 + 3 lateral setae. Dens dorsally crenulate. Mucronal seta absent. Trunk colour distributed uniformly.

hadriaticus
Background colour dark brownish or black. Colour black. Trunk colour distributed uniformly.

maculatus
Pigment pattern in irregular patches. Pigmentation as irregular symmetrical patches on tergites. Trunk colour concentrated in distinctive patterns.

nebulosus
Relative length of antennal segments i:ii:iii:iv are as 60:78:80:82. Mesochaetae smooth. Body with thin violet drawings mostly present on last abdominal tergites. Legs whitish. Manubrium with many short setae and two longer ones on dorsal side and with several ventral mesochaetae, which are mostly distributed on the distal margin. Dentes with few microchaetae on the ventral side. Dentes dorsally with two microsensilla. Dentes dorsally with many short setae, which are longer on lateral margins. Furca: retinaculum with 14 to 32 ordinary setae. Habitus: body length: 2 mm. Head: labium with 10 to 15 setae on each part of submentum. Head: postantennal organ rounded. Head: postantennal organ/dca: 0. 6–0. 8. Irregular stripes violet. L/antennae: 2. 25. Legs: tibiotarsal chaetotaxy composed of smooth ordinary setae and several slightly ciliate macrochaetae. Pigment pattern in irregular patches. Pigmentation as irregular stripes on posterior part of third to fifth abdominal segments. Submentum with 10 + 10 to 15 + 15 setae. Tibiotarsal macrochaetae slightly ciliate. Trunk colour concentrated in distinctive patterns.

palustris
Abdominal setae all smooth. Lateral flaps of ventral tube with 3 + 3 setae. Longitudinal middorsal pattern less than 1/5 width of tergites and sometimes absent on the last abdominal tergites. Longitudinal middorsal pattern interrupted or fainter, especially on third abdominal segment, with net-like ornaments on lateral parts of each tergite. Mucro without lateral seta. Pigment pattern longitudinal. Pigment pattern in regular bands. Trunk colour concentrated in distinctive patterns. Unguiculus with inner corner tooth.

plumosus 2
Abdominal setae some smooth and some weakly feathered having 3 to 5 ciliae laterally near the base of the seta, especially abundant on third abdominal segment. Lateral flaps of ventral tube with 3 + 3 setae. Longitudinal middorsal pattern less than 1/5 width of tergites and sometimes absent on the last abdominal tergites. Longitudinal middorsal pattern interrupted or fainter, especially on third abdominal segment, with net-like ornaments on lateral parts of each tergite. Mucro with lateral seta. Pigment pattern longitudinal. Pigment pattern in regular bands. Trunk colour concentrated in distinctive patterns. Unguiculus without inner tooth.

prasinus
Background colour light greenish or yellowish. Collophore with up to 20 + 20 lateral setae. Dens dorsally tuberculate. Mucronal seta present. Trunk colour distributed uniformly.

pseudopalustris 1
Dorsolateral pigmentation abundant brownish. Lateral flaps of ventral tube with 3 + 3 setae. Longitudinal middorsal pattern less than 1/5 width of tergites and sometimes absent on the last abdominal tergites. Longitudinal middorsal pattern continuous and very pronounced, sometimes absent on fifth and sixth abdominal segment. Pigment pattern longitudinal. Pigment pattern in regular bands. Trunk colour concentrated in distinctive patterns.

rabili
Pigment pattern transversal. Pigment pattern in regular bands. Pigmentation dark on all tergites of second thoracic segment to second abdominal segment, completely covered. Trunk colour concentrated in distinctive patterns.

unifasciatus
Dorsolateral pigmentation absent or very limited. Lateral flaps of ventral tube with 3 + 3 setae. Longitudinal middorsal pattern less than 1/5 width of tergites and sometimes absent on the last abdominal tergites. Longitudinal middorsal pattern continuous and very pronounced, sometimes absent on fifth and sixth abdominal segment. Pigment pattern longitudinal. Pigment pattern in regular bands. Trunk colour concentrated in distinctive patterns.


References