Axonchium Cobb, 1920

Kumar, Sumit & Ahmad, Wasim, 2023, Six new and four known species of the genus Axonchium Cobb, 1920 (Nematoda: Dorylaimida: Belondiroidea) from the Western Ghats of India, European Journal of Taxonomy 857, pp. 1-56 : 46-52

Key to species of the genus Axonchium Cobb, 1920 (based on females) (modified after Naz & Ahmad 2012)

1. Lips completely amalgamated ........................................................................................................... 2

– Lips incompletely separated or well separated.................................................................................. 3

2. Body length 1.2–1.4 mm; anterior uterine branch present ..................... A. perplexans Siddiqi, 1995

– Body length 1.5–1.6 mm; anterior uterine branch absent........... A. tochigiense Khan & Araki, 2002

3. The inner portion of the lips deeply offset and appearing as subspherical liplets............................... .................................................................................................................... A. labiatum Thorne, 1939

– The inner portion of the lips less offset and marked by depression of the contour........................... 4

4. Odontostyle straight and narrow; anterior part of pharynx very narrow; pharyngeal constriction inconspicuous; body pores numerous................................................................................................... 5

– Odontostyle fusiform; anterior part of pharynx quite muscular; pharyngeal constriction very deep or isthmus-like; body pores few............................................................................................................. 6

5. Body length 1.8–2.0 mm; odontostyle 8–10 µm; uterus without ‘Z’-organ........................................ ................................................................................................... A. geminum Coomans & Nair, 1975

– Body length 2.6–3.8 mm; odontostyle 10.5–15 µm; uterus with ‘Z’-organ........................................ .................................................................................................... A. variabile Coomans & Nair, 1975

6. Vulva broad, lengthwise oval; vaginal lumen adjacent to vulva very wide; pharyngeal constriction short isthmus-like................................................ A. propinquum ( de Man,1921) sensu Thorne 1939

– Vulva transverse, broad or narrow; vaginal lumen narrow; pharyngeal constriction deep or rarely isthmus-like........................................................................................................................................ 7

7. Intestino-prerectal junction marked by a constriction, surrounded by a sphincter-like structure........ .................................................................................................................... A. cingulatum Nair, 1973

– Constriction or sphincter-like structure at the intestino-prerectal junction absent ............................ 8

8. Anterior genital branch less than ¾ of the corresponding body diameter long................................. 9

– Anterior genital branch usually long, very rarely slightly less than the body diameter long .......... 12

9. Vagina straight, vaginal cuticle wide with rounded or spheroid walls .. A. bulbosum Williams, 1958

– Vagina bent posteriad, vaginal cuticle not wide .............................................................................. 10

10. Body slender (body width 27–35 µm); lips with a shallow notch in the middle separating the outer and inner portions ..................................................................................... A. nitidum Jairajpuri, 1964

– Body rather stout (body width 41–58 µm); lips with a deep notch in the middle separating the outer and inner portions .............................................................................................................................11

11. Expanded part of pharynx 74–80% of total neck length; anterior uterine branch rudimentary; tail hemispherical with clavate end and 3 caudal pores on each side ........................................................ ............................................................................................ A. camelliae Dhanam & Jairajpuri, 1998

– Expanded part of pharynx 55–73% of total neck length; anterior uterine branch a simple sac; tail convex-conoid to bluntly rounded and 2 caudal pores on each side ................................................... .................................................................................................................... A. amplicolle Cobb, 1920

12. Posterior genital branch with ‘Z’-organ................................................ A. bihariense Popovici, 1990

– Posterior genital branch without ‘Z’-organ ..................................................................................... 13

13. Vagina with a constriction in the middle ......................................................................................... 14

– Vagina without constriction, or gradually widening towards the uterus ......................................... 24

14. Expanded part of pharynx short, about 39–49% of total neck length; tail bluntly conoid .................. .............................................................................................................................. A. indicum sp. nov.

– Expanded part of pharynx long, more than 50% of total neck length; tail hemispheroid ............... 15

15. Vagina wall appears somewhat darker than and offset from the body cuticle..................................... ............................................................................................................... A. saccatum Jairajpuri, 1964

– Vaginal cuticle not differentiated from the body cuticle.................................................................. 16

16. Body length 1.0– 1.7 mm ................................................................................................................. 17

– Body length 1.8–2.8 mm ................................................................................................................. 21

17. Body almost straight, 1.1–1.3 mm long; anterior uterine sac 1.7–2.3 times corresponding body diameter long; tail obtusely rounded ......................................................... A. microspiculum sp. nov.

– Body slightly ventrally arcuate or straight, over 1.3 mm long; anterior uterine sac more than 2.3 times the body diameter; tail hemispheroid..................................................................................... 18

18. Vagina straight; anterior uterine branch a simple sac without proximal constriction.......................... ................................................................................. A. thoubalicum Dhanachand & Jairajpuri, 1981

– Vagina straight or slightly to completely directed posteriad; anterior uterine branch provided with a proximal constriction....................................................................................................................... 19

19. Body almost straight; vaginal wall distinctly thicker than the body cuticle, vaginal sphincter well developed................................................................. A. phukani Rahman, Jairajpuri & Ahmad, 1985

– Body slightly ventrally arcuate; vaginal wall almost of same thickness as the body cuticle, vaginal sphincter weakly developed............................................................................................................. 20

20. Odontostyle 8–9 µm ............................................. A. neoeletum Rahman, Jairajpuri & Ahmad, 1985

– Odontostyle 11–12 µm......................................................................................... A. tropicum sp. nov.

21. Vagina straight; anterior uterine sac without a proximal constriction ................................................. ............................................................................. A.khasianum Rahman, Jairajpuri & Ahmad, 1985

– Vagina bent posteriad; anterior uterine sac with a proximal constriction........................................ 22

22. Body length 2.1–2.8 mm; middle tubular part of uterus very narrow ................ A. heynsi Nair, 1973

– Body length 1.8–2.2 mm; middle tubular part of uterus wide......................................................... 23

23. Body almost straight; vaginal lumen becoming cross-shaped within the sphincter; anterior uterine branch 2–3 times body diameter long....................................................... A. transkeiense Nair, 1973

– Body curved ventrad; vaginal lumen narrow and straight; anterior uterine branch 3–4 times body diameter long.................................................. A. parasaccatum Rahman, Jairajpuri & Ahmad, 1985

24. Vaginal lumen highly expanded toward the uterus, with diamond-shaped lumen in lateral view ...... ................................................................................................................. A. paracingulatum sp. nov.

– Vaginal lumen moderately expanded............................................................................................... 25

25. Lip region distinctly wide (13–15 µm); odontophore more than 1.5 times the odontostyle length .... .............................................................................................. A. sinclairi Heyns & Furstenberg, 1993

– Lip region narrow (less than 12 µm); odontophore less than 1.5 times the odontostyle length...... 26

26. Body almost straight........................................................................................................................ 27

– Body ventrally arcuate..................................................................................................................... 28

27. Lip region high, with conoid lips; cardia more or less heart-shaped; tail broadly conoid, shorter than anal body diameter.................................. A. sabulum ( Yeates, 1967) sensu Coomans & Yeates 1969

– Lip region low, with small offset inner portions of the lips; cardia cylindrical; tail cylindroid, longer than the anal body diameter................................................................... A. latespiculatum Nair, 1973

28. Body more than 2 mm long; cardia linguiform; posterior uterus with very narrow tubular part........ ................................................................................. A. manalicum Ali, Jairajpuri & Coomans, 1974

– Body 2 mm or less; cardia rounded to heart-shaped........................................................................ 29

29. Vagina completely directed posteriad.............................................................................................. 30

– Vagina slightly inclined posteriad.................................................................................................... 32

30. Lip region with incompletely separated lips and amalgamated inner parts......................................... ....................................................................................................... A. siddiqii Coomans & Nair, 1975

– Lip region with well separated lips and separated inner parts......................................................... 31

31. Vagina about two-thirds of the corresponding body diameter; prerectum 3.5–6.5 times anal body diameter; tail hemispheroid to almost clavate .............................. A. noreasum Naz & Ahmad, 2012

– Vagina large, more than two-thirds of the corresponding body diameter; prerectum 7–12 times anal body diameter; tail bluntly conoid.................................................................... A. nilgiriense sp. nov.

32. Anterior part of pharynx slender, separated from the posterior expanded part by an isthmus-like constriction ............................................................................ A. meghalayense Naz & Ahmad, 2012

– Anterior part of pharynx moderately to highly muscular, separated from the posterior expanded part by a constriction, isthmus-like structure absent............................................................................... 33

33. Anterior part of pharynx moderately muscular, separated from the posterior expanded part by a weak constriction; tail broadly rounded, distinctly clavate due to expansion of cuticle............................... .......................................................................................... A. cooverkolli Dhanam & Jairajpuri, 1998

– Anterior part of pharynx quite muscular, separated from the posterior expanded part by a very distinct constriction; tail not clavate..................................................................................................... 34

34. Prerectum 10–13 times anal body diameter long; tail bluntly rounded, slightly clavate .................... ............................................................................................ A. hosakodii Dhanam & Jairajpuri, 1998

– Prerectum less than 10 times anal body diameter long; tail rounded or hemispheroid ................... 35

35. Expanded part of pharynx 60% or less of total neck length; tail obtusely rounded ............................ .................................................................................................................. A. elegans Jairajpuri, 1964

– Expanded part of pharynx more than 60% of total neck length; tail hemispherical or broadly rounded.................................................................................................................................................... 36

36. Body length 1.3–1.4 mm ................................................................ A. shamimi Baqri & Khera, 1976

– Body more than 1.5 mm long .......................................................................................................... 37

37. Body length 1.5–1.6 mm; odontostyle 7–9 µm; anterior genital branch without proximal constriction .................................................................................... A. eletum Dhanachand & Jairajpuri, 1981

– Body length 1.6–1.9 mm; odontostyle 10.5–12 µm; anterior genital branch with proximal constriction ................................................................................................................................................... 38

38. Lip region with well separated lips; odontostyle 1.1–1.3 times lip region width long........................ ............... A. metobtusicaudatum (Sch.Stekhoven & Teunissen, 1938) sensu Nair & Coomans 1973

– Lip region with incompletely separated lips; odontostyle about lip region width long .................. 39

39. Lip region low, bluntly conoid; tail bluntly conoid with rounded terminus.......... A. uniqum sp. nov.

– Lip region moderately high, rounded; tail hemispherical........... A. vallum Ahmad & Jairajpuri,1982

Key to species of the genus Axonchium Cobb, 1920 (based on males) (modified after Naz & Ahmad, 2012)

1. Lip region offset with incompletely separated lips........................................................................... 2

– Lip region offset with well separated lips......................................................................................... 4

2.– Body more than 1.5 mm long; odontostyle 10–12 µm; spicules 55–57 µm........................................ ................................................................................................... A. vallum Ahmad & Jairajpuri, 1982

Body about or less than 1.5 mm long; odontostyle 8–9 µm; spicules less than 40 µm..................... 3

3. Spicules 36–39 µm; ventromedian supplements 7; lateral guiding pieces 13–15 µm........................ ....................................................................................................... A. shamimi Baqri & Khera, 1976

– Spicules 32 µm; ventromedian supplements 2; lateral guiding pieces 10 µm.................................... ...................................................................................................... A. siddiqii Coomans & Nair, 1975

4. Over 150 lateral and over 80 ventral body pores; 7–10 caudal pores; spicules very stout, 52–71 µm long with almost straight ventral side; anterior pharynx very slender................................................ ................................................................................................... A. variabile Coomans & Nair, 1975

– Body pores less numerous; up to 4 caudal pores.............................................................................. 5

5. First ventromedian supplement above the range of spicules............................................................ 6

– First ventromedian supplement within the range of spicules ......................................................... 16

6. Ventromedian supplements 2............................................................................................................ 7

– Ventromedian supplements 4 or more .............................................................................................. 8

7. Spicules 20–23 µm, regular in shape........................................................ A. microspiculum sp. nov.

– Spicules 30–36 µm, proximally slender about two-fifths of the total spicule length, and distal part comparatively robust ................................................................... A. noreasum Naz & Ahmad, 2012

8. Tail about 1.2 anal body diameter long; spicules short and stout, with greatest width in distal half and complex median piece without posterior projection; lateral guiding pieces less than 10 µm, very heavily sclerotized, without distal bifurcation...................................... A. latespiculatum Nair, 1973

– Tail one or less than one anal body width long; spicules stout with simple median piece and posterior projection at the distal end; lateral guiding pieces more than 10 µm, with distal bifurcation... 9

9. Spicules longer, 1.7–1.9 cloacal body diameter long, ventromedian supplements 4 ......................... ....................................................................... A. parasaccatum Rahman, Jairajpuri & Ahmad, 1985

– Spicules 1.5 or less cloacal body diameter long; supplements 4 or more ...................................... 10

10. Spicules bent ventrally with bluntly rounded distal ends, inner walls heavily sclerotized .............11

– Spicules arcuate, weakly sclerotized .............................................................................................. 13

11. Spicules 1.2 cloacal body diameter long, proximal end of spicules less thickened, median piece thin at most of its length, swollen near distal end.......... A. thoubalicum Dhanachand & Jairajpuri, 1981

– Spicules 1.2–1.4 cloacal body diameter long, median piece of spicules not swollen near distal end ........................................................................................................................................................ 12

12. Body 2.1–2.8 mm long; spicules bent ventrally at right angle, stout with blunt posterior projection at distal end, inner walls of spicules sometimes crenate; 5–10 ventromedian supplements .............. ........................................................................................................................... A. heynsi Nair, 1973

– Body 1.4–1.7 mm long; spicules slightly ventrally curved without posterior projection at distal end, inner walls of spicules uniformly thickened; 4–6 ventromedian supplements................................... ................................................................................ A. phukani Rahman, Jairajpuri & Ahmad, 1985

13. Body 1.6 mm long; expanded part of pharynx 50–54% of total neck length; lateral guiding pieces with sclerotized bifid tip .................................................... A. hosakodii Dhanam & Jairajpuri, 1998

– Body 1.7–2.0 mm long; expanded part of pharynx more than 60% of total neck length; lateral guiding pieces with bifurcated distal ends........................................................................................... 14

14. Body L-shaped; 6–7 irregularly spaced ventromedian supplements; lateral guiding pieces swollen with diverging distal ends; tail with three caudal pores on each side..... A. transkeiense Nair, 1973

– Body slightly curved ventrad; 5–7 regularly spaced ventromedian supplements; lateral guiding pieces with bifurcated distal ends; tail with two caudal pores on each side................................... 15

15. Spicules 1.2 cloacal body diameter long; prerectum 11–14 cloacal body diameter long; 6–7 regularly spaced ventromedian supplements; tail one anal body width long ................................................ ........................................................................... A. khasianum Rahman, Jairajpuri & Ahmad, 1985

– Spicules 1.5 cloacal body diameter long; prerectum 6 anal body diameter long; 5 regularly spaced ventromedian supplements; tail about 0.7 anal body diameter long .................................................. ................................................................................................ A. meghalyense Naz & Ahmad, 2012

16. Spicules slender .............................................................................................................................. 17

– Spicules robust................................................................................................................................ 20

17. Lip region 9–10 µm wide; spicules somewhat sickle-shaped, its dorsal contour with irregularly convex bulge at level of hump.............................................................................. A. uniqum sp. nov.

– Lip region more than 11–15 µm wide; spicules simple in shape, dorsal contour regularly convex.... 18

18. Spicules 50–56 µm long; ventromedian supplements 5–6 ................................................................. ............................................................... A. sabulum ( Yeates, 1967) sensu Coomans & Yeates 1969

– Spicules more than 70 µm long; ventromedian supplements 7–12 ................................................ 19

19. Guiding ring ‘double’; 7–11 irregularly spaced ventromedian supplements; spicules 78–81 µm, ventrally arcuate, head of spicules distinctly ventrally curved; lateral guiding pieces arcuate.......... ............................................................................................. A. sinclairi Heyns & Furstenberg, 1993

– Guiding ring single; 8–12 ventromedian supplements in two groups; spicules 73–79 µm, ventrally arcuate, head of spicules not ventrally curved; lateral guiding pieces slender, straight ..................... ..................................................................................................................... A. dubium Siddiqi, 1995

20. Spicules large, 66–70 µm long ....................................................................................................... 21

– Spicules 55 µm or less long............................................................................................................ 22

21. Body 2.5–2.8 mm long; first ventromedian supplement just in front of proximal end of spicules; spicules strongly bent ventrally at right angle, inner walls of spicules crenate................................... ................................................................................................................. A. paracingulatum sp. nov.

– Body 1.9–2.0 mm long; 5 ventromedian supplements posterior to proximal end of spicules; spicules ventrally curved, inner walls of spicules smooth, not crenate; lateral guiding pieces rod-like and provided with a distal inward projection ................ A. manalicum Ali, Jairajpuri & Coomans, 1974

22. Body 1.2–1.3 mm long; spicules less than 33 µm long.................................................................. 23

– Body 1.4–2.2 mm long; spicules more than 39 µm long................................................................ 24

23. Spicules unusually wide at the blunt distal end; lateral guiding pieces with bifid distal ends; tail with two caudal pores on each side ................................................................. A. elegans Jairajpuri, 1964

– Spicules with narrow distal end; lateral guiding pieces with blunt distal ends; tail with three caudal pores on each side............................................................ A. cooverkolli Dhanam & Jairajpuri, 1998

24. Spicules strongly arcuate; lateral guiding pieces ventrally arcuate with thickened distal end; tail bluntly conoid .................................................................................................. A. nilgiriense sp. nov.

– Spicules not strongly arcuate; lateral guiding pieces straight with bifurcated distal end; tail hemispherical rounded or convex conoid................................................................................................. 25

25. Spicules with wide distal end ......................................................................................................... 26

– Spicules with narrow distal end...................................................................................................... 29

26. Spicules 39–44 µm or 1.0–1.1 cloacal body diameter long with very broad and truncate distal end .............................................................................................................. A. saccatum Jairajpuri, 1964

– Spicules over 1.5 cloacal body diameter long with blunt distal end .............................................. 27

27. 9 ventromedian supplements in two groups of three and six; first supplements posterior to the proximal end of spicules; lateral guiding pieces weakly sclerotized .......................................................... ......................................................................................... A. eletum Dhanachand & Jairajpuri, 1981

– 4–8 irregularly spaced ventromedian supplements; first supplement just in front of spicules; lateral guiding pieces heavily sclerotized .................................................................................................. 28

28. Odontostyle 11–12 µm long; ventromedian supplements 4; lateral guiding pieces simple rod-like with bifurcated distal end.................................................................................... A. tropicum sp. nov.

– Odontostyle 8–9 µm long; ventromedian supplements more than 4; lateral guiding pieces slightly curved in proximal region.................................... A. neoeletum Rahman, Jairajpuri & Ahmad, 1985

29. Ventromedian supplements 10–13; lateral guiding pieces slender; prerectum 9.4–12.2 anal body widths long; tail with 4 caudal pores on each side ............................................................................. .......................................................................... A. propinquum ( de Man, 1921) sensu Thorne 1939

– Ventromedian supplements less than 10; lateral guiding pieces not so slender; prerectum less than 10 anal body widths long; tail with 2 caudal pores on each side.................................................... 30

30. Prerectum 4.3–7.4 anal body widths long; lateral guiding pieces simple with bifurcated distal ends ................................................................................................................... A. amplicolle Cobb, 1920

– Prerectum 8.7–9.9 anal body diameters long; lateral guiding pieces with thickened distal end ........ .............. A. metobtusicaudatum (Sch.Stekhoven & Teunissen, 1938) sensu Nair & Coomans 1973

Not included in key due to unavailability of literature

A. cephalatum (Schuurmans Stekhoven, 1951) Andrássy, 1986 .

A. monhysteroides ( Altherr, 1974) Andrássy, 1990 .

A. subeletum Gambhir & Dhanachand, 1990 .