Checklist of the Collembola: Key to the genera of Onychiurinae

http://www.collembola.org/key/onycinae.htm - Last updated on 2009.09.30 by Frans Janssens

Checklist of the Collembola: Key to the genera of Onychiurinae

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.

Romuald J. Pomorski, Zoological Institute, Wroclaw University, Pl-50-335 Wroclaw, Poland
Kenneth A. Christiansen, Department of Biology, Grinnell College, Grinnell, IA 50112-0806, USA
Yulija B. Sveenkova, State Nature Reserve "Privolzhskaya Lesostep" Okruzhnaya 12a, 440008 Penza, Russia
David Steinmann, Boulder, Colorado 80302, USA
Frans Janssens, Department of Biology, University of Antwerp, Antwerp, B-2020, Belgium

Introduction

In this subfamily are included all Onychiuridae with the furcula rudimentary or absent, no dark pigment, and four or more papillae in an apical organ on the third antennal segment (Fig. Intro.A).

Fig.Intro. Characteristics useful in identification of Onychiurinae
A. Location of postantennal organ and third antennal segment sense organ
c - sense club, r - sense rod, p - paddle shaped sensilla
B. Typical distribution of ventral pseudocelli; left side, species with more numerous pseudocelli
C. Dividing line between dorsal and ventral pseudocelli
D. Forms of parapseudocelli
Characters found most useful in classification are:

Apical organ of the third antennal segment: number of papillae and guard setae, form of sense clubs. See Fig. Intro.A for the location of this organ.
Post antennal organ (P.A.O.): shape, arrangement, and number of tubercles. See Fig. Intro.A. Both the organs are frequently difficult to make out; we have found them easiest to study in well-flattened specimens, or in temporary mounts in which the specimen can be rolled to the proper orientation.
Pseudocelli: number and arrangement on the head and first 8 trunk segments. There is some confusion in the literature as to the dorsal or ventral position of the more lateral pseudocelli; Fig. Intro.C shows the dividing line which has been used to separate dorsal and ventral pseudocelli. The pseudocellus indicated by the arrow has been assigned previously to either the fourth or fifth abdominal segments; it is here placed arbitrarily on the fourth. The ventral pseudocelli are often obscure and hard to locate; Fig. Intro.B&C shows in diagrammatic fashion 2 typical patterns of distribution. As pseudocelli are recognised only those circular or oval areas with smooth or ridged inner surfaces; similar areas with finely granulate inner surfaces are considered to be foveae.
Parapseudocelli (Fig. Intro.D). These organs resemble pseudocelli but they are long and slit like or elongate elliptical. They always lack the chitinized border common in pseudocelli. They are generally limited to ventral surfaces, legs and anal lobes.
Chaetotaxy: this appears to be stable in some species and quite variable in others; the variation may be partly geographic and may include sexual dimorphism. General form and differentiation of setae and their arrangement on the fifth abdominal tergite, second abdominal sternite, and antennae have been found useful in certain species. This character is worth much more attention.
Structure of the unguiculus, and occasionally of the unguis and tenent hairs.
Presence or absence, and structure, of the anal spines.
Integumentary granulation: apply to the dorsal surface of the head and the tergites, and generally neglect the finer areas of granulation on the intersegmental membranes and in the foveae.
The male ventral organ: this is made up of 1 or more groups of setae, slightly to highly modified, on the venter of 1 or more of abdominal segments 2, 3, and 4. Not all species have this structure and even when present it is developed only in mature males, but in certain groups it provides the best feature for species recognition. The organ often continues to differentiate in additional molts after sexual maturity.
The presence or absence and form of the vestiges of the furcula.
Microsensilla which occur on the lateral margins of the thorax are of taxonomic importance.

Most of these characters are best seen in dorsoventrally flattened specimens.

Note: The key does not include the genus Pseudonychiurus Bagnall, 1948. The settlement of taxonomic position of this genus at this moment is impossible. Typical species - Aphorura dentata Folsom, 1902 should be redescribed.

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). Posterior cephalic pseudocelli absent (fig.1a).............. 2 Posterior cephalic pseudocelli present (fig.1b)............ 11

Fig.1.

2(1). Third antennal segment sense organ with 4-5 papilla, no papilla-like prominence................................... 3 Third antennal segment sense organ with 5 papilla and additional papilla-like prominence (fig.2)............... 9

Fig.2.

3(2). Third abdominal tergum with submedial pseudocelli........... 4 Third abdominal tergum without submedial pseudocelli........ 8

4(3). Furca reduced to finely granulated area with setulae posteriorly tenaculum absent.............................. 5 Furca reduced to two knobs with 3 + 3 or 4 + 4 setulae...... 7

5(4). Labium with 4 papillae, lateral 'E' papilla absent (fig.3b); third antennal segment sense organ with 4 guard setae (fig.3a)..................................... Hymenaphorura Labium with 5 papillae, lateral 'E' papilla present (fig.3d); third antennal segment sense organ with 5 guard setae (fig.3c)................................................. 6

Fig.3.

6(5). Body with very distinct parapseudocelli; granular areas of fourth abdominal tergum fused together midline into one plate (fig.4a); labium type 'A' thickened and apically blunt........................................... Sacaphorura Body without parapseudocelli; granular areas on fourth abdominal tergum separated by 2 medial parallel rows of smaller granules (fig.4b); labium type '0' - with all 5 papillae apically pointed....................... Vexaphorura

Fig.4.

7(4). Anterior cephalic pseudocelli located inside antennal area (fig.5a); body fusiform (fig.6a).............. Kalaphorura Anterior cephalic pseudocelli located outside of antennal area (fig.5b); body oval-elliptical (fig.6b)..... Psyllaphorura

Fig.5.

Fig.6.

8(3). Chaetotaxy on terga consists of one kind of setae: all setae apically pointed; furca reduced to a small area of fine granulation with 4 setulae arranged in one row or an arch located in a middle part of sternum iv (fig.7b); vesicles in postantennal organ of three kinds - simple, bilobed or multilobed - located perpendicularly or obliquely to the long axis of the organ........................ Heteraphorura Chaetotaxy on terga consists of two kinds of setae: blunt rod-like mesosetae and pointed microsetae; furca reduced to a small depression with 2 small, posterior setae, in contact with the border between abdominal sterna iii and iv (fig.7a); vesicles in postantennal organ compound.......... ............................................. Paronychiurus

Fig.7.

9(2). Furca reduced to a small concavity without granulation; pseudocelli absent; tibiotarsi with 11 distal setae...... 10 Furca reduced to a small depression without granulation with 2 setulae posteriorly; pseudocelli present; tibiotarsi with 9 distal setae........................................ Arneria

10(9). Body with parapseudocelli always located outside of areas of coarser granulation; macrosetae rod-like and apically blunt; vestigial furcal area with 4 setulae posteriorly arranged in one row......................................... Dinochiurus Body without parapseudocelli; macrosetae apically pointed; vestigial furcal area with 2 setulae posteriorly. Reducturus

11(1). Body with lateral pseudocelli (fig.1b)..................... 12 Body without lateral pseudocelli (fig.1a)...... Probolaphorura

12(11). Postantennal organ fully developed (fig.8b-e).............. 13 Postantennal organ reduced to long furrow, without vesicles (fig.8a)...................................... Cribrochiurus

Fig.8.

13(12). Postantennal organ with 3-5 lobes of one vesicle (fig.8b).. 14 Postantennal organ with 8 or more vesicles (fig.8c-e)...... 17

14(13). Tibiotarsi with clavate setae in distal whorl (fig.9)........ ........................................... Chribellphorura Tibiotarsi with typical acuminate setae in distal whorl.... 15

Fig.9.

15(14). Anal spines absent............................... Archaphorura Anal spines present........................................ 16

16(15). Furca reduced to cuticular furrow or finely granulated area with 1 + 1 setulae posteriorly (fig.10b, c).... Micraphorura Furca reduced to cuticular furrow or finely granulated area with 2 + 2 setulae posteriorly (fig.10a)....... Oligaphorura

Fig.10.

17(13). Seta d0 on the head absent (fig.11a)........................ 18 Seta d0 on the head present (fig.11b)....................... 25

Fig.11.

18(17). Vesicles in postantennal organ compound (fig.8d)........... 19 Vesicles in postantennal organ simple (fig.8c)............. 20

19(18). Sense organ of third antennal segment with more then three guard setae...................................... Detriturus Sense organ of third antennal segment with only three guard setae..................................... Sensillonychiurus

20(18). Anal spines absent......................................... 21 Anal spines present........................................ 22

21(20). Pseudocelli elevated (fig.12)................. Similonychiurus Pseudocelli not elevated......................... Spelaphorura

Fig.12.

22(20). Furca reduced to finely granulated area........... Megaphorura Furca vestigial............................................ 23

23(22). Furca reduced to cuticular pocket with 2 + 2 or 1 + 1 setulae (fig.13b)................................................ 24 Furca reduced to two knobs with rudiment of mucro (fig.13a)... .............................................. Supraphorura

Fig.13.

24(23). Microsensillum of fourth antennal segment located at the level of second row of setae......................... Protaphorura ² Microsensillum of fourth antennal segment located on the basal part of apical third.......................... Yoshiiphorura ¹

25(17). Furca reduced to finely granulated area with 2 + 2 setulae in one row (fig.14c) or 1 + 1 setulae posteriorly (fig.14d), or to cuticular pocket with 2 + 2 setulae (fig.15b)......... 26 Furca reduced to finely granulated area with 2 + 2 setulae in two rows posteriorly (fig.15a)........................... 35

Fig.14.

Fig.15.

26(25). Claw as long as antenna; third antennal segment sense organ with two rows of guard papillae............. Ongulonychiurus Claw as long as first proximal antennal segment; third antennal segment sense organ with one row of guard papillae. ........................................................ 27

27(26). Distal whorl of setae on tibiotarsi with 11 pointed setae (fig.16a)................................................ 28 Distal whorl of setae on tibiotarsi with 9 or 7 pointed setae (fig.16b, c)............................................. 33

Fig.16.

28(27). Furca reduced to cuticular pocket with 2 + 2 setulae (fig.14b)...................................... Bionychiurus Furca reduced to finely granulated area with 1 + 1 setulae posteriorly (fig.14d), or without trace of furca......... 29

29(28). Body feebly plurichaetotic; microsensillum of fourth antennal segment near its base.................................... 30 Body strongly plurichaetotic; microsensillum of fourth antennal segment near its apex.................... Absolonia

30(29). Head with 2 + 2 posterior pseudocelli.......... Vibronychiurus Head with at least 3 + 3 posterior pseudocelli, if only 3 + 3 pseudocelli always arranged in a triangle................ 31

31(30). Anal spines absent......................................... 32 Anal spines present............................ Deharvengiurus

32(31). Terga with multiplication of pseudocelli........ Argonychiurus Terga with typical 3-4 pseudocelli.............. Onychiuroides

33(27). Anal spines absent......................................... 34 Anal spines present................................ Onychiurus

34(33). Dorsal sense organ of third antennal segment with 5 papilla and bent sensory clubs (fig.17a); furca reduced to finely granulated area with 2 + 2 setulae posteriorly arranged in one row (fig.14c)............................ Deuteraphorura Dorsal sense organ of third antennal segment with straight sensory clubs and usually with 4 papilla (fig.17b); furca reduced to finely granulated area with 1 + 1 setulae posteriorly (fig.14d)........................ Orthonychiurus

Fig.17.

35(25). Distal whorl of setae on tibiotarsi with 7 setae (fig.16c). 36 Distal whorl of setae on tibiotarsi with more than 7 setae. 37

36(35). Anal spines absent................................ Agraphorura Anal spines present.......................... Tantulonychiurus

37(35). Vesicles in postantennal organ compound.................... 38 Vesicles in postantennal organ simple......... Thalassaphorura

38(37). Anal spines seta-like located without papillae. Micronychiurus Anal spines strong on distinct papillae......... Allonychiurus

Endnotes

¹. Most of the diagnostic characters of this genus are removed, because true Protaphorura species have similar structure of furcal fold, with protergal pseudocelli and multiplication of setae on abdominal tergum VI (a last character is connected with large size of species - ca. 3 mm). The localization of the microsensillum is left as diagnostic, because this character is not found in true Protaphorura. Yoshiiphorura is a very good example of erection of a paraphiletic genus. The synonymisation of the genus in this key would be illegal, so it will be done in a printed publication.

². The genus Heteronychiurus is synonymised it with Protaphorura (Pomorski, Leithner & Brucken, 2003:311).


1(0). Posterior cephalic pseudocelli absent (fig.1a).............. 2 Posterior cephalic pseudocelli present (fig.1b)............ 11
Fig.1.
2(1). Third antennal segment sense organ with 4-5 papilla, no papilla-like prominence................................... 3 Third antennal segment sense organ with 5 papilla and additional papilla-like prominence (fig.2)............... 9
Fig.2.
3(2). Third abdominal tergum with submedial pseudocelli........... 4 Third abdominal tergum without submedial pseudocelli........ 8
4(3). Furca reduced to finely granulated area with setulae posteriorly tenaculum absent.............................. 5 Furca reduced to two knobs with 3 + 3 or 4 + 4 setulae...... 7
5(4). Labium with 4 papillae, lateral 'E' papilla absent (fig.3b); third antennal segment sense organ with 4 guard setae (fig.3a)..................................... Hymenaphorura Labium with 5 papillae, lateral 'E' papilla present (fig.3d); third antennal segment sense organ with 5 guard setae (fig.3c)................................................. 6
Fig.3.
6(5). Body with very distinct parapseudocelli; granular areas of fourth abdominal tergum fused together midline into one plate (fig.4a); labium type 'A' thickened and apically blunt........................................... Sacaphorura Body without parapseudocelli; granular areas on fourth abdominal tergum separated by 2 medial parallel rows of smaller granules (fig.4b); labium type '0' - with all 5 papillae apically pointed....................... Vexaphorura
Fig.4.
7(4). Anterior cephalic pseudocelli located inside antennal area (fig.5a); body fusiform (fig.6a).............. Kalaphorura Anterior cephalic pseudocelli located outside of antennal area (fig.5b); body oval-elliptical (fig.6b)..... Psyllaphorura
Fig.5.
Fig.6.
8(3). Chaetotaxy on terga consists of one kind of setae: all setae apically pointed; furca reduced to a small area of fine granulation with 4 setulae arranged in one row or an arch located in a middle part of sternum iv (fig.7b); vesicles in postantennal organ of three kinds - simple, bilobed or multilobed - located perpendicularly or obliquely to the long axis of the organ........................ Heteraphorura Chaetotaxy on terga consists of two kinds of setae: blunt rod-like mesosetae and pointed microsetae; furca reduced to a small depression with 2 small, posterior setae, in contact with the border between abdominal sterna iii and iv (fig.7a); vesicles in postantennal organ compound.......... ............................................. Paronychiurus
Fig.7.
9(2). Furca reduced to a small concavity without granulation; pseudocelli absent; tibiotarsi with 11 distal setae...... 10 Furca reduced to a small depression without granulation with 2 setulae posteriorly; pseudocelli present; tibiotarsi with 9 distal setae........................................ Arneria
10(9). Body with parapseudocelli always located outside of areas of coarser granulation; macrosetae rod-like and apically blunt; vestigial furcal area with 4 setulae posteriorly arranged in one row......................................... Dinochiurus Body without parapseudocelli; macrosetae apically pointed; vestigial furcal area with 2 setulae posteriorly. Reducturus
11(1). Body with lateral pseudocelli (fig.1b)..................... 12 Body without lateral pseudocelli (fig.1a)...... Probolaphorura
12(11). Postantennal organ fully developed (fig.8b-e).............. 13 Postantennal organ reduced to long furrow, without vesicles (fig.8a)...................................... Cribrochiurus
Fig.8.
13(12). Postantennal organ with 3-5 lobes of one vesicle (fig.8b).. 14 Postantennal organ with 8 or more vesicles (fig.8c-e)...... 17
14(13). Tibiotarsi with clavate setae in distal whorl (fig.9)........ ........................................... Chribellphorura Tibiotarsi with typical acuminate setae in distal whorl.... 15
Fig.9.
15(14). Anal spines absent............................... Archaphorura Anal spines present........................................ 16
16(15). Furca reduced to cuticular furrow or finely granulated area with 1 + 1 setulae posteriorly (fig.10b, c).... Micraphorura Furca reduced to cuticular furrow or finely granulated area with 2 + 2 setulae posteriorly (fig.10a)....... Oligaphorura
Fig.10.
17(13). Seta d0 on the head absent (fig.11a)........................ 18 Seta d0 on the head present (fig.11b)....................... 25
Fig.11.
18(17). Vesicles in postantennal organ compound (fig.8d)........... 19 Vesicles in postantennal organ simple (fig.8c)............. 20
19(18). Sense organ of third antennal segment with more then three guard setae...................................... Detriturus Sense organ of third antennal segment with only three guard setae..................................... Sensillonychiurus
20(18). Anal spines absent......................................... 21 Anal spines present........................................ 22
21(20). Pseudocelli elevated (fig.12)................. Similonychiurus Pseudocelli not elevated......................... Spelaphorura
Fig.12.
22(20). Furca reduced to finely granulated area........... Megaphorura Furca vestigial............................................ 23
23(22). Furca reduced to cuticular pocket with 2 + 2 or 1 + 1 setulae (fig.13b)................................................ 24 Furca reduced to two knobs with rudiment of mucro (fig.13a)... .............................................. Supraphorura
Fig.13.
24(23). Microsensillum of fourth antennal segment located at the level of second row of setae......................... Protaphorura ² Microsensillum of fourth antennal segment located on the basal part of apical third.......................... Yoshiiphorura ¹
25(17). Furca reduced to finely granulated area with 2 + 2 setulae in one row (fig.14c) or 1 + 1 setulae posteriorly (fig.14d), or to cuticular pocket with 2 + 2 setulae (fig.15b)......... 26 Furca reduced to finely granulated area with 2 + 2 setulae in two rows posteriorly (fig.15a)........................... 35
Fig.14.
Fig.15.
26(25). Claw as long as antenna; third antennal segment sense organ with two rows of guard papillae............. Ongulonychiurus Claw as long as first proximal antennal segment; third antennal segment sense organ with one row of guard papillae. ........................................................ 27
27(26). Distal whorl of setae on tibiotarsi with 11 pointed setae (fig.16a)................................................ 28 Distal whorl of setae on tibiotarsi with 9 or 7 pointed setae (fig.16b, c)............................................. 33
Fig.16.
28(27). Furca reduced to cuticular pocket with 2 + 2 setulae (fig.14b)...................................... Bionychiurus Furca reduced to finely granulated area with 1 + 1 setulae posteriorly (fig.14d), or without trace of furca......... 29
29(28). Body feebly plurichaetotic; microsensillum of fourth antennal segment near its base.................................... 30 Body strongly plurichaetotic; microsensillum of fourth antennal segment near its apex.................... Absolonia
30(29). Head with 2 + 2 posterior pseudocelli.......... Vibronychiurus Head with at least 3 + 3 posterior pseudocelli, if only 3 + 3 pseudocelli always arranged in a triangle................ 31
31(30). Anal spines absent......................................... 32 Anal spines present............................ Deharvengiurus
32(31). Terga with multiplication of pseudocelli........ Argonychiurus Terga with typical 3-4 pseudocelli.............. Onychiuroides
33(27). Anal spines absent......................................... 34 Anal spines present................................ Onychiurus
34(33). Dorsal sense organ of third antennal segment with 5 papilla and bent sensory clubs (fig.17a); furca reduced to finely granulated area with 2 + 2 setulae posteriorly arranged in one row (fig.14c)............................ Deuteraphorura Dorsal sense organ of third antennal segment with straight sensory clubs and usually with 4 papilla (fig.17b); furca reduced to finely granulated area with 1 + 1 setulae posteriorly (fig.14d)........................ Orthonychiurus
Fig.17.
35(25). Distal whorl of setae on tibiotarsi with 7 setae (fig.16c). 36 Distal whorl of setae on tibiotarsi with more than 7 setae. 37
36(35). Anal spines absent................................ Agraphorura Anal spines present.......................... Tantulonychiurus
37(35). Vesicles in postantennal organ compound.................... 38 Vesicles in postantennal organ simple......... Thalassaphorura
38(37). Anal spines seta-like located without papillae. Micronychiurus Anal spines strong on distinct papillae......... Allonychiurus

http://www.collembola.org/key/onycinae.htm - Last updated on 2009.09.30 by Frans Janssens

Introduction

Rationale

Key

References