http://www.collembola.org/key/caecus.htm - Last updated on 2017.06.30 by Frans Janssens
Checklist of the Collembola: Key to the species of the caecus group of Arrhopalites

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.

Robert S. Vargovitsh, Schmalhausen Institute of Zoology NAS of Ukraine, Kiev, 01601, Ukraine
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).   Cuticular spines on sixth abdominal segment absent.......... 2
        Cuticular spines on sixth abdominal segment present........ 10
 
2(1).   Fourth antennal segment subdivided and adjoining subsegments
          separated by several rings................................ 3
        Fourth antennal segment undivided or its adjoining subsegments
          separated by one ring..................................... 7
 
3(2).   Antenna 2 times or more longer than head; tunica on third claw
          absent.................................................... 4
        Antenna about 1.5x of head; tunica on third claw present......
           ............................................... karabiensis 2
 
4(3).   Claws extremely long........................................ 5
        Claws not extremely long.................................... 6
 
5(4).   Seta ms5 on sixth abdominal segment absent; setae of head
          dorsum slender; antenna about 2 times of head...... macronyx
        Seta ms5 on sixth abdominal segment present; setae of head
          dorsum stout; antenna about 3x of head.................. gul
 
6(4).   Circumanal setae broadened and mps3 present; fourth antennal
          segment with 13 whorls of setae; head dorsum with 9
          spine-like setae; third antennal segment with subbasal
          swelling......................................... abchasicus 1
        Circumanal setae not broadened and mps3 absent; fourth
          antennal segment with 15 whorls of setae; head dorsum with 5
          spine-like setae; third antennal segment not swelled........
           ................................................ peculiaris
 
7(2).   Anterodistal seta of dens Ia not or weakly spine-like; fourth
          antennal segment undivided................................ 8
        Anterodistal seta of dens Ia strongly spine-like; fourth
          antennal segment with 3-4 subsegments............. ulehlovae
 
8(7).   Eyes 1 + 1.................................................. 9
        Eyes absent........................................ pukouensis
 
9(8).   Circumanal axial seta ms1 forked..................... coreanus
        Circumanal axial seta ms1 not forked.................... minor
 
10(1).  Sixth abdominal segment with 5 + 5 cuticular spines. antrobius
        Sixth abdominal segment with at most 4 + 4 cuticular spines...
           ........................................................ 11
 
11(10). Fourth antennal segment subdivided and adjoining subsegments
          of fourth antennal segment separated by several rings.... 12
        Fourth antennal segment undivided or its adjoining subsegments
          separated by one ring.................................... 13
 
12(11). Antenna 2 times of head; empodia not reaching tip of
          corresponding claw; hind claw without tunica; seta ms5 on
          sixth abdominal segment absent................... abchasicus
        Antenna about 1.5x of head; empodia overtopping tip of
          corresponding claw; hind claw with tunica; seta ms5 on sixth
          abdominal segment present....................... karabiensis
 
13(11). Sixth abdominal segment with 4 + 4 cuticular spines........ 14
        Sixth abdominal segment with at most 3 + 3 cuticular spines...
           ........................................................ 17
 
14(13). Fourth antennal segment undivided or very indistinctly divided
          into pseudosubsegments................................... 15
        Fourth antennal segment with 4 distinct ringed subsegments....
           .................................................. incertus
 
15(14). Antenna 1.5x or less of head............................... 16
        Antenna about 2 times of head......................... minutus
 
16(15). First claw with inner tooth............................ caecus
        First claw without inner tooth......................... millsi
 
17(13). Empodium of first legi with distinct corner tooth; sixth
          abdominal segment usually with 3 + 3 cuticular spines.......
           .................................................... tenuis
        Empodium of first legi without corner tooth; sixth abdominal
          segment with 2 + 2 cuticular spines.................. loczyi

Endnotes

1 Possession of cuticular spines on the sixth abdominal segment is variable in abchasicus.

2 Possession of cuticular spines on the sixth abdominal segment is variable in karabiensis.


Differential diagnoses

abchasicus
Antenna 2 times of head. Cuticular spines on sixth abdominal segment present. Empodia not reaching tip of corresponding claw. Fourth antennal segment subdivided and adjoining subsegments of fourth antennal segment separated by several rings. Hind claw without tunica. Seta ms5 on sixth abdominal segment absent. Sixth abdominal segment with at most 4 + 4 cuticular spines.

abchasicus 1
Antenna 2 times or more longer than head. Circumanal setae broadened and mps3 present. Claws not extremely long. Cuticular spines on sixth abdominal segment absent. Fourth antennal segment subdivided and adjoining subsegments separated by several rings. Fourth antennal segment with 13 whorls of setae. Head dorsum with 9 spine-like setae. Third antennal segment with subbasal swelling. Tunica on third claw absent.

antrobius
Cuticular spines on sixth abdominal segment present. Sixth abdominal segment with 5 + 5 cuticular spines.

caecus
Antenna 1.5x or less of head. Cuticular spines on sixth abdominal segment present. First claw with inner tooth. Fourth antennal segment undivided or its adjoining subsegments separated by one ring. Fourth antennal segment undivided or very indistinctly divided into pseudosubsegments. Sixth abdominal segment with 4 + 4 cuticular spines. Sixth abdominal segment with at most 4 + 4 cuticular spines.

coreanus
Anterodistal seta of dens Ia not or weakly spine-like. Circumanal axial seta ms1 forked. Cuticular spines on sixth abdominal segment absent. Eyes 1 + 1. Fourth antennal segment undivided or its adjoining subsegments separated by one ring. Fourth antennal segment undivided.

gul
Antenna 2 times or more longer than head. Antenna about 3x of head. Claws extremely long. Cuticular spines on sixth abdominal segment absent. Fourth antennal segment subdivided and adjoining subsegments separated by several rings. Seta ms5 on sixth abdominal segment present. Setae of head dorsum stout. Tunica on third claw absent.

incertus
Cuticular spines on sixth abdominal segment present. Fourth antennal segment undivided or its adjoining subsegments separated by one ring. Fourth antennal segment with 4 distinct ringed subsegments. Sixth abdominal segment with 4 + 4 cuticular spines. Sixth abdominal segment with at most 4 + 4 cuticular spines.

karabiensis
Antenna about 1.5x of head. Cuticular spines on sixth abdominal segment present. Empodia overtopping tip of corresponding claw. Fourth antennal segment subdivided and adjoining subsegments of fourth antennal segment separated by several rings. Hind claw with tunica. Seta ms5 on sixth abdominal segment present. Sixth abdominal segment with at most 4 + 4 cuticular spines.

karabiensis 2
Antenna about 1.5x of head. Cuticular spines on sixth abdominal segment absent. Fourth antennal segment subdivided and adjoining subsegments separated by several rings. Tunica on third claw present.

loczyi
Cuticular spines on sixth abdominal segment present. Empodium of first legi without corner tooth. Fourth antennal segment undivided or its adjoining subsegments separated by one ring. Sixth abdominal segment with 2 + 2 cuticular spines. Sixth abdominal segment with at most 3 + 3 cuticular spines. Sixth abdominal segment with at most 4 + 4 cuticular spines.

macronyx
Antenna 2 times or more longer than head. Antenna about 2 times of head. Claws extremely long. Cuticular spines on sixth abdominal segment absent. Fourth antennal segment subdivided and adjoining subsegments separated by several rings. Seta ms5 on sixth abdominal segment absent. Setae of head dorsum slender. Tunica on third claw absent.

millsi
Antenna 1.5x or less of head. Cuticular spines on sixth abdominal segment present. First claw without inner tooth. Fourth antennal segment undivided or its adjoining subsegments separated by one ring. Fourth antennal segment undivided or very indistinctly divided into pseudosubsegments. Sixth abdominal segment with 4 + 4 cuticular spines. Sixth abdominal segment with at most 4 + 4 cuticular spines.

minor
Anterodistal seta of dens Ia not or weakly spine-like. Circumanal axial seta ms1 not forked. Cuticular spines on sixth abdominal segment absent. Eyes 1 + 1. Fourth antennal segment undivided or its adjoining subsegments separated by one ring. Fourth antennal segment undivided.

minutus
Antenna about 2 times of head. Cuticular spines on sixth abdominal segment present. Fourth antennal segment undivided or its adjoining subsegments separated by one ring. Fourth antennal segment undivided or very indistinctly divided into pseudosubsegments. Sixth abdominal segment with 4 + 4 cuticular spines. Sixth abdominal segment with at most 4 + 4 cuticular spines.

peculiaris
Antenna 2 times or more longer than head. Circumanal setae not broadened and mps3 absent. Claws not extremely long. Cuticular spines on sixth abdominal segment absent. Fourth antennal segment subdivided and adjoining subsegments separated by several rings. Fourth antennal segment with 15 whorls of setae. Head dorsum with 5 spine-like setae. Third antennal segment not swelled. Tunica on third claw absent.

pukouensis
Anterodistal seta of dens Ia not or weakly spine-like. Cuticular spines on sixth abdominal segment absent. Eyes absent. Fourth antennal segment undivided or its adjoining subsegments separated by one ring. Fourth antennal segment undivided.

tenuis
Cuticular spines on sixth abdominal segment present. Empodium of first legi with distinct corner tooth. Fourth antennal segment undivided or its adjoining subsegments separated by one ring. Sixth abdominal segment usually with 3 + 3 cuticular spines. Sixth abdominal segment with at most 3 + 3 cuticular spines. Sixth abdominal segment with at most 4 + 4 cuticular spines.

ulehlovae
Anterodistal seta of dens Ia strongly spine-like. Cuticular spines on sixth abdominal segment absent. Fourth antennal segment undivided or its adjoining subsegments separated by one ring. Fourth antennal segment with 3–4 subsegments.


References