See Table 4 for additional diagnostic characters.
1. Amphidial fovea a transverse slit; cuticle with ten longitudinal ridges .... Edalonema Andrássy, 2007
– Amphidial fovea double-loop-shaped in male, unispiral in female .................. Belgopeltula gen. nov.
– Amphidial fovea unispiral ................................................................................................................ 2
– Amphidial fovea loop-shaped ........................................................................................................... 4
2. Basal bulb absent; freshwater or terrestrial ........................................ Cylindrolaimus de Man, 1880
– Basal bulb present; marine ................................................................................................................ 3
3. Single anterior ovary ................................................................ Intasia Tchesunov & Miljutina, 2008
– Two ovaries (anterior and posterior) ....................................................... Southerniella Allgén, 1932
4. Oral opening shifted to the ventral body side ............................ Morlaxia Vincx & Gourbault, 1988
– Oral opening apical or shifted to the dorsal body side ..................................................................... 5
5. Basal pharyngeal bulb present; ovaries antidromously reflexed ............... Mudwigglus Leduc, 2013
– Basal pharyngeal bulb absent; ovaries outstretched ......................................................................... 6
6. Lateral alae present, in some species fused with the ventral limb of the amphid ............................... ................................................................................................................... Campylaimus Cobb, 1920
– Lateral alae absent ............................................................................................................................ 7
7. Amphid in a shape of rounded loop .................................................................................................. 8
– Amphid in a shape of elongated loop ............................................................................................. 10
8. Anterior body region abruptly narrowing; amphid at a distance equal to more than five labial region diameters from the anterior end ............................................. Metaraeolaimoides De Coninck, 1936
– Anterior body region cylindrical or subcylindrical; amphid at a distance equal to less than two labial region diameters from the anterior end ............................................................................................. 9
9. Buccal cavity cup-shaped; pronounced sexual dimorphism in the amphid size (large in males and small in females) .................................................................................. Pararaeolaimus Timm, 1961 – Buccal cavity conical; no sexual dimorphism in the amphid size .......... Araeolaimus de Man, 1888
10. Cervical (paramphideal) setae absent; caudal glands open via three separate pores .......................... ................................................................................................................. Diplopeltula Gerlach, 1950
– Cervical (paramphideal) setae present; caudal glands open via common spinneret ........................11
11. Amphid located on a well-developed refractive subcuticular plate .................................................... .......................................................................................... Diplopeltis Cobb in Stiles & Hassal, 1905
– Refractive subcuticular plate absent .......................................... Pseudaraeolaimus Chitwood, 1951