Metadesmolaimus, Schuurmans Stekhoven, 1935

Li, Ting, Ban, Shuyan & Huang, Yong, 2023, Two new species of Xyalidae Chitwood, 1951 (Nematoda, Monhysterida) from Chinese Sea Area, Zootaxa 5369 (2), pp. 255-268 : 265-266

Dichotomous key to the species of Metadesmolaimus (modified from Guo et al. 2016)

1. Spicules slender and elongated, longer than two cloacal body diameters.......................................... 2

- Spicules not elongated, shorter than 1.6 cloacal body diameters................................................. 3

2. Body 1.6 mm long, amphids 0.6 head diameter from anterior end............................................................................................... M. caniculus ( Wieser & Hopper, 1967) Gerlach & Riemann, 1973

- Body 0.8–1.1 mm, amphids 1 head diameter from anterior end............................ M. varians Lorenzen, 1971

3. Tail conical.......................................................................................... 4

- Tail conico-cylindrical................................................................................. 7

4. Somatic setae long and dense, spicules slightly bent with tooth-shaped distal end.................................................................................................... M. hamatus ( Gerlach, 1956) Lorenzen, 1971

- Somatic setae shorter than 0.6 corresponding body diameter, spicules arcuated, distal end not tooth-shaped.............. 5

5. Both spicules distinctly unequal in length.......................................... M. heteroclitus Lorenzen, 1971

- Both spicules equal in length............................................................................ 6

6. Amphids small, 32%–36% corresponding body diameter in diameter, spicules relatively slender, 1.5–1.6 cloacal body diameters long............................................................................... M. gaelicus Platt, 1983

- Amphids large, 50% corresponding body diameter in diameter, spicules broad, 1.3 cloacal body diameters long............................................................................. M. tersus ( Gerlach, 1956) Lorenzen, 1971

7. Tail elongated, nine cloacal body diameters long........................... M. coronatus Schuurmans Stekhoven, 1950

- Tail not elongated, shorter than seven cloacal body diameters.................................................. 8

8. Pharynx with 18 bulb-like muscular swellings.............................................. M. bulbosus sp. nov.

- Pharynx even without bulb-like muscular swelling........................................................... 9

9. Somatic setae dense and long........................................................................... 10

- Somatic setae sparse and short.......................................................................... 13

10. Outer labial setae jointed, distal end of spicules not hooked......................... M. zhanggi Guo, Chen & Liu, 2016

- Outer labial setae unjointed, distal end of spicules hooked.................................................... 11

11. Gubernaculum absent....................................................... M. psammophilus Tchesunov, 1990

- Gubernaculum present................................................................................ 12

12. Body slightly slender (a=32–37), spicules 32 µm (shorter than 1.4 cloacal body diameters)...... M. aduncus Lorenzen, 1971

- Body slightly stout (a=25–29), spicules 44–46 µm (1.5 cloacal body diameters)................................................................................................ M. gelana ( Warwick & Platt, 1973) Lorenzen, 1977

13. Amphids larger than 60% corresponding body diameter in diameter......................... M. pandus Lorenzen, 1971

- Amphids smaller than 50% corresponding body diameter in diameter........................................... 14

14. Cephalic setae shorter than 0.5 head diameter, amphids close to anterior end (less than 1 head diameter from anterior end)................................................................................ M. communis Gagarin, 2013

- Cephalic setae longer than 0.6 head diameter, amphids further from anterior end (longer than 1.5 head diameters from anterior end)............................................................................................... 15

15. Cervical setae longer than 1 corresponding body diameter, gubernaculum broad................ M. elegans Gagarin, 2013

- Cervical setae shorter than 0.5 corresponding body diameter, gubernaculum strip-like or sleeve shaped................ 16

16. Spicules arcuated with terminal teeth, gubernaculum strip-like............................ M. similis Tchesunov, 1990

- Spicules L-shaped, gubernaculum sleeve-shaped surrounding distal half of spicules.......... M. aversivulva Gerlach, 1953