http://www.collembola.org/key/megaloth.htm - Last updated on 2013.09.11 by Frans Janssens
Checklist of the Collembola: Key to the species of Megalothorax

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.

Clément Schneider, Dpt Systématique & Evolution, Muséum national d'Histoire naturelle, F-75005 Paris, France
Cyrille D'Haese, Dpt Systématique & Evolution, Muséum national d'Histoire naturelle, F-75005 Paris, France
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).   Mucro posterior edges perfectly smooth (fig.1a) or rather
          smooth with irregularities (fig.1b)...................... 2
        Mucro posterior edges serrate (fig.1c, d) or crenelate
          (fig.1e)................................................ 12

Fig.1.
   
2(1).   Mucro large with wide edges, elliptical at least in posterior
          view (fig.2a, b)........................................ 3
        Mucro with thin edges, not elliptical, no part of the mucro
          significantly larger than the basis....................... 5

Fig.2.
   
3(2).   Retinaculum with 3 + 3 teeth........................ aquaticus
        Retinaculum with 4 + 4 teeth................................ 4
 

4(3).   Labral a-chaetae serrate, almost twice as long as m-chaetae
          (fig.3b); mucro, in posterior view, largest part at 3/5
          from basis and apically pointed (fig.2a); pigmentation
          more or less deep reddish........................... rubidus
        Labral a-chaetae smooth, about twice as long as m-chaetae
          (fig.3a); mucro, in posterior view, largest part 2/5 from
          basis (fig.4); pigmentation absent.............. granulosus

Fig.3.
  

Fig.4.
   
5(2).   Sensilla Sg of third antennal segment absent............. poki
        Sensilla Sg of third antennal segment present (fig.5)...... 6

Fig.5.
   
6(5).   Special inner sensillum of sensory field 2 to 6 globular
          (fig.6a).................................................. 7
        Special inner sensillum of sensory field 2 to 6 not globular..
           ......................................................... 8

Fig.6.
   
7(6).   Labral chaetae a1 forked (fig.7b); mucro posterior edges
          mostly smooth with possible faint teeth or irregularities
          (fig.1b)............................................ piloli
        Labral chaetae a1 not forked (fig.7a); mucro perfectly
          smooth (fig.8)................................ interruptus

Fig.7.
  

Fig.8.
   
8(6).   Chaeta X of fourth antennal segment absent (fig.9a, b);
          channels on forehead with multiple forks (fig.10a, b)..... 9
        Chaeta X of fourth antennal segment present (fig.9c);
          channels on forehead simple, without fork (fig.10c)...... 10

Fig.9.
  

Fig.10.
   
9(8).   Chaeta a0 on forehead absent, replaced with a tegumentary oval
          protuberance (fig.10a); chaeta X absent, not replaced by
          tegumentary process on fourth antennal segment; claws of
          ordinary proportions; third antennal segment with six
          ordinary chaetae (fig.11a).................. sanctistephani
        Chaeta a0 present, no oval protuberance on forehead (fig.10b);
          chaeta X absent, replaced by a tegumentary process on fourth
          antennal segment; claws long and thin (fig.12); third
          antennal segment with eight ordinary chaetae (fig.11b).....
           .............................................. tuberculatus

Fig.11.
  

Fig.12.
   
10(8).  Chaetae on back of head relatively strong and long (fig.13b);
          mucro wider on the basal 3/5, thinner on the apical 2/5
          (fig.14); secondary granulation without pattern........... 11
        Chaetae on back of head short and thin (fig.13a); mucro wider
          basally on 6/8 of length, then getting suddenly thinner
          (fig.1a); secondary granulation laterally on abdomen with
          specific pattern (fig.15).................... svalbardensis

Fig.13.
  

Fig.14.
  

Fig.15.
   
11(10). Inner sensillum of sensory field 2 - 6 all candle flame-shaped
          (fig.16a, b); pigmentation absent; sensilla s2 rather big...
           ................................................... willemi
        Inner sensillum of sensory field 2 - 6 some T-shaped (fig.6b);
          pigmentation often brown or orange; sensilla s2 rather
          small............................................... minimus

Fig.16.
   
12(1).  Mucro serrate on the whole length or almost the whole length,
          never crenelated......................................... 13
        Mucro serrate or crenelate, but smooth on the apical part 1/4
          or more of the mucro length (fig.1c, e)................. 21
 

13(12). Dens with 3 to 4 chaetae; abdominal dorsal microchaetae
          numerous...................................... spinotricosus
        Dens with no more than two posterior chaetae (fig.17),
          sometime less, no anterior chaetae; abdominal dorsal
          microchaetae absent...................................... 14

Fig.17.
   
14(13). Second antennal segment with 4 chaetae..................... 15
        Second antennal segment with 6 chaetae................ tonoius
 

15(14). Labral a-chaetae large and strongly serrate (fig.18a, b);
          posterior chaetae on the head all 7 + 7 very strong
          (fig.19a, b)............................................ 16
        Labral a-chaetae with subtle teeth (fig.18c); posterior
          chaetae on the head max 3 + 3 much stronger than the
          remaining chaetae (fig.19c, d).......................... 17

Fig.18.
  

Fig.19.
   
16(15). Distal subsegment of dens almost as long as mucro (fig.20);
          empodial tubercle well-developed; labral chaeta m0 on the
          level of other m-chaetae, a-row and m-row close to each
          other; labral chaetae a1 with one strong tooth at 1/2 of the
          apex, almost bifid (fig.18b); labral chaetae a2 with one
          tooth............................................. australis
        Distal subsegment of dens clearly shorter than mucro
          (fig.17); empodial tubercle weakly developed (fig.12);
          labral chaeta m0 moved forward in intermediate position
          between a-row and m-row (fig.18a); labral chaetae a1 with
          three external teeth near the apex; labral chaetae a2 with
          two teeth......................................... rapoporti

Fig.20.
   
17(15). Chaetae on back of head and abdomen ordinary; sensilla s3
          present.................................................. 18
        Chaetae on back of head, thorax and abdomen some strong and
          long, sword-like (fig.21a, b); sensilla s3 absent. massoudi

Fig.21.
   
18(17). Body pigmentation absent or only weakly present; mucro rather
          thin; size of adult max 0.5 mm........................... 19
        Body pigmentation white with black pigment dots clearly
          visible under the field microscope, condensed dorsally on
          head and abdomen; mucro rather large (fig.1d); size of
          adult max 0.6 mm............................. nigropunctatus
 

19(18). Body not pigmented or slightly reddish; mucro teeth rather
          large.................................................... 20
        Body with weak dots of black pigment hardly visible on field
          microscope; mucro teeth thin and subtle........ perspicillum
 

20(19). Empodial tubercle not or feebly protruding (fig.22b); body
          sometimes with subtle reddish pigmentation......... incertus
        Empodial tubercle protruding (fig.22a); body not pigmented...
           .................................................. tristani

Fig.22.
   
21(12). Mucro crenelate smooth apically 1/4 of the mucro (fig.1e)....
           ................................................ gabonensis
        Mucro serrate smooth apically 1/3 of the mucro (fig.1c)......
           .................................................... boneti

Endnotes

1 M. laevis Denis, 1948, M. albus Maynard, 1951 and M. maculosus Maynard, 1951 are excluded from this key for which no reliable diagnostic characteristics could be found in the original descriptions.

Differential diagnoses

aquaticus
Mucro large with wide edges, elliptical at least in posterior view (fig.2a, b). Mucro posterior edges perfectly smooth (fig.1a) or rather smooth with irregularities (fig.1b). Retinaculum with 3 + 3 teeth.

australis
Abdominal dorsal microchaetae absent. Dens with no more than two posterior chaetae (fig.17), sometime less, no anterior chaetae. Distal subsegment of dens almost as long as mucro (fig.20). Empodial tubercle well-developed. Labral a-chaetae large and strongly serrate (fig.18a, b). Labral chaeta m0 on the level of other m-chaetae, a-row and m-row close to each other. Labral chaetae a1 with one strong tooth at 1/2 of the apex, almost bifid (fig.18b). Labral chaetae a2 with one tooth. Mucro posterior edges serrate (fig.1c, d) or crenelate (fig.1e). Mucro serrate on the whole length or almost the whole length, never crenelated. Posterior chaetae on the head all 7 + 7 very strong (fig.19a, b). Second antennal segment with 4 chaetae.

boneti
Mucro serrate smooth apically 1/3 of the mucro (fig.1c). Mucro posterior edges serrate (fig.1c, d) or crenelate (fig.1e). Mucro serrate or crenelate, but smooth on the apical part 1/4 or more of the mucro length (fig.1c, e).

gabonensis
Mucro crenelate smooth apically 1/4 of the mucro (fig.1e). Mucro posterior edges serrate (fig.1c, d) or crenelate (fig.1e). Mucro serrate or crenelate, but smooth on the apical part 1/4 or more of the mucro length (fig.1c, e).

granulosus
Labral a-chaetae smooth, about twice as long as m-chaetae (fig.3a). Mucro large with wide edges, elliptical at least in posterior view (fig.2a, b). Mucro posterior edges perfectly smooth (fig.1a) or rather smooth with irregularities (fig.1b). Mucro, in posterior view, largest part 2/5 from basis (fig.4). Pigmentation absent. Retinaculum with 4 + 4 teeth.

incertus
Abdominal dorsal microchaetae absent. Body not pigmented or slightly reddish. Body sometimes with subtle reddish pigmentation. Body pigmentation absent or only weakly present. Chaetae on back of head and abdomen ordinary. Dens with no more than two posterior chaetae (fig.17), sometime less, no anterior chaetae. Empodial tubercle not or feebly protruding (fig.22b). Labral a-chaetae with subtle teeth (fig.18c). Mucro posterior edges serrate (fig.1c, d) or crenelate (fig.1e). Mucro rather thin. Mucro serrate on the whole length or almost the whole length, never crenelated. Mucro teeth rather large. Posterior chaetae on the head max 3 + 3 much stronger than the remaining chaetae (fig.19c, d). Second antennal segment with 4 chaetae. Sensilla s3 present. Size of adult max 0.5 mm.

interruptus
Labral chaetae a1 not forked (fig.7a). Mucro with thin edges, not elliptical, no part of the mucro significantly larger than the basis. Mucro perfectly smooth (fig.8). Mucro posterior edges perfectly smooth (fig.1a) or rather smooth with irregularities (fig.1b). Sensilla Sg of third antennal segment present (fig.5). Special inner sensillum of sensory field 2 to 6 globular (fig.6a).

massoudi
Abdominal dorsal microchaetae absent. Chaetae on back of head, thorax and abdomen some strong and long, sword-like (fig.21a, b). Dens with no more than two posterior chaetae (fig.17), sometime less, no anterior chaetae. Labral a-chaetae with subtle teeth (fig.18c). Mucro posterior edges serrate (fig.1c, d) or crenelate (fig.1e). Mucro serrate on the whole length or almost the whole length, never crenelated. Posterior chaetae on the head max 3 + 3 much stronger than the remaining chaetae (fig.19c, d). Second antennal segment with 4 chaetae. Sensilla s3 absent.

minimus
Chaeta X of fourth antennal segment present (fig.9c). Chaetae on back of head relatively strong and long (fig.13b). Channels on forehead simple, without fork (fig.10c). Inner sensillum of sensory field 2 – 6 some T-shaped (fig.6b). Mucro with thin edges, not elliptical, no part of the mucro significantly larger than the basis. Mucro posterior edges perfectly smooth (fig.1a) or rather smooth with irregularities (fig.1b). Mucro wider on the basal 3/5, thinner on the apical 2/5 (fig.14). Pigmentation often brown or orange. Secondary granulation without pattern. Sensilla Sg of third antennal segment present (fig.5). Sensilla s2 rather small. Special inner sensillum of sensory field 2 to 6 not globular.

nigropunctatus
Abdominal dorsal microchaetae absent. Body pigmentation white with black pigment dots clearly visible under the field microscope, condensed dorsally on head and abdomen. Chaetae on back of head and abdomen ordinary. Dens with no more than two posterior chaetae (fig.17), sometime less, no anterior chaetae. Labral a-chaetae with subtle teeth (fig.18c). Mucro posterior edges serrate (fig.1c, d) or crenelate (fig.1e). Mucro rather large (fig.1d). Mucro serrate on the whole length or almost the whole length, never crenelated. Posterior chaetae on the head max 3 + 3 much stronger than the remaining chaetae (fig.19c, d). Second antennal segment with 4 chaetae. Sensilla s3 present. Size of adult max 0.6 mm.

perspicillum
Abdominal dorsal microchaetae absent. Body with weak dots of black pigment hardly visible on field microscope. Body pigmentation absent or only weakly present. Chaetae on back of head and abdomen ordinary. Dens with no more than two posterior chaetae (fig.17), sometime less, no anterior chaetae. Labral a-chaetae with subtle teeth (fig.18c). Mucro posterior edges serrate (fig.1c, d) or crenelate (fig.1e). Mucro rather thin. Mucro serrate on the whole length or almost the whole length, never crenelated. Mucro teeth thin and subtle. Posterior chaetae on the head max 3 + 3 much stronger than the remaining chaetae (fig.19c, d). Second antennal segment with 4 chaetae. Sensilla s3 present. Size of adult max 0.5 mm.

piloli
Labral chaetae a1 forked (fig.7b). Mucro with thin edges, not elliptical, no part of the mucro significantly larger than the basis. Mucro posterior edges mostly smooth with possible faint teeth or irregularities (fig.1b). Mucro posterior edges perfectly smooth (fig.1a) or rather smooth with irregularities (fig.1b). Sensilla Sg of third antennal segment present (fig.5). Special inner sensillum of sensory field 2 to 6 globular (fig.6a).

poki
Mucro with thin edges, not elliptical, no part of the mucro significantly larger than the basis. Mucro posterior edges perfectly smooth (fig.1a) or rather smooth with irregularities (fig.1b). Sensilla Sg of third antennal segment absent.

rapoporti
Abdominal dorsal microchaetae absent. Dens with no more than two posterior chaetae (fig.17), sometime less, no anterior chaetae. Distal subsegment of dens clearly shorter than mucro (fig.17). Empodial tubercle weakly developed (fig.12). Labral a-chaetae large and strongly serrate (fig.18a, b). Labral chaeta m0 moved forward in intermediate position between a-row and m-row (fig.18a). Labral chaetae a1 with three external teeth near the apex. Labral chaetae a2 with two teeth. Mucro posterior edges serrate (fig.1c, d) or crenelate (fig.1e). Mucro serrate on the whole length or almost the whole length, never crenelated. Posterior chaetae on the head all 7 + 7 very strong (fig.19a, b). Second antennal segment with 4 chaetae.

rubidus
Labral a-chaetae serrate, almost twice as long as m-chaetae (fig.3b). Mucro large with wide edges, elliptical at least in posterior view (fig.2a, b). Mucro posterior edges perfectly smooth (fig.1a) or rather smooth with irregularities (fig.1b). Mucro, in posterior view, largest part at 3/5 from basis and apically pointed (fig.2a). Pigmentation more or less deep reddish. Retinaculum with 4 + 4 teeth.

sanctistephani
Chaeta X absent, not replaced by tegumentary process on fourth antennal segment. Chaeta X of fourth antennal segment absent (fig.9a, b). Chaeta a0 on forehead absent, replaced with a tegumentary oval protuberance (fig.10a). Channels on forehead with multiple forks (fig.10a, b). Claws of ordinary proportions. Mucro with thin edges, not elliptical, no part of the mucro significantly larger than the basis. Mucro posterior edges perfectly smooth (fig.1a) or rather smooth with irregularities (fig.1b). Sensilla Sg of third antennal segment present (fig.5). Special inner sensillum of sensory field 2 to 6 not globular. Third antennal segment with six ordinary chaetae (fig.11a).

spinotricosus
Abdominal dorsal microchaetae numerous. Dens with fig. to 4 chaetae. Mucro posterior edges serrate (fig.1c, d) or crenelate (fig.1e). Mucro serrate on the whole length or almost the whole length, never crenelated.

svalbardensis
Chaeta X of fourth antennal segment present (fig.9c). Chaetae on back of head short and thin (fig.13a). Channels on forehead simple, without fork (fig.10c). Mucro with thin edges, not elliptical, no part of the mucro significantly larger than the basis. Mucro posterior edges perfectly smooth (fig.1a) or rather smooth with irregularities (fig.1b). Mucro wider basally on 6/8 of length, then getting suddenly thinner (fig.1a). Secondary granulation laterally on abdomen with specific pattern (fig.15). Sensilla Sg of third antennal segment present (fig.5). Special inner sensillum of sensory field 2 to 6 not globular.

tonoius
Abdominal dorsal microchaetae absent. Dens with no more than two posterior chaetae (fig.17), sometime less, no anterior chaetae. Mucro posterior edges serrate (fig.1c, d) or crenelate (fig.1e). Mucro serrate on the whole length or almost the whole length, never crenelated. Second antennal segment with 6 chaetae.

tristani
Abdominal dorsal microchaetae absent. Body not pigmented or slightly reddish. Body not pigmented. Body pigmentation absent or only weakly present. Chaetae on back of head and abdomen ordinary. Dens with no more than two posterior chaetae (fig.17), sometime less, no anterior chaetae. Empodial tubercle protruding (fig.22a). Labral a-chaetae with subtle teeth (fig.18c). Mucro posterior edges serrate (fig.1c, d) or crenelate (fig.1e). Mucro rather thin. Mucro serrate on the whole length or almost the whole length, never crenelated. Mucro teeth rather large. Posterior chaetae on the head max 3 + 3 much stronger than the remaining chaetae (fig.19c, d). Second antennal segment with 4 chaetae. Sensilla s3 present. Size of adult max 0.5 mm.

tuberculatus
Chaeta X absent, replaced by a tegumentary process on fourth antennal segment. Chaeta X of fourth antennal segment absent (fig.9a, b). Chaeta a0 present, no oval protuberance on forehead (fig.10b). Channels on forehead with multiple forks (fig.10a, b). Claws long and thin (fig.12). Mucro with thin edges, not elliptical, no part of the mucro significantly larger than the basis. Mucro posterior edges perfectly smooth (fig.1a) or rather smooth with irregularities (fig.1b). Sensilla Sg of third antennal segment present (fig.5). Special inner sensillum of sensory field 2 to 6 not globular. Third antennal segment with eight ordinary chaetae (fig.11b).

willemi
Chaeta X of fourth antennal segment present (fig.9c). Chaetae on back of head relatively strong and long (fig.13b). Channels on forehead simple, without fork (fig.10c). Inner sensillum of sensory field 2 – 6 all candle flame-shaped (fig.16a, b). Mucro with thin edges, not elliptical, no part of the mucro significantly larger than the basis. Mucro posterior edges perfectly smooth (fig.1a) or rather smooth with irregularities (fig.1b). Mucro wider on the basal 3/5, thinner on the apical fig.14/5 (fig.14). Pigmentation absent. Secondary granulation without pattern. Sensilla Sg of third antennal segment present (fig.5). Sensilla s2 rather big. Special inner sensillum of sensory field 2 to 6 not globular.

References