Key to valid species of the genus Promonhystera .

1. Spicules slightly straight or arcuated, not double curved....................................................... 2

- Spicules double curved, wave-shaped..................................................................... 5

2. Precloacal supplements papilliform, spicules equal or longer than 170 μm........................... P. papilla sp. nov.

- Precloacal supplements absent, spicules shorter than 100 μm................................................... 3

3. Body length shorter than 1 mm, spicules 26–27 µm or 1.4–1.6 cloacal body diameter long.... P. crinita Leduc & Zhao, 2023

- Body length longer than 1 mm, spicules 58–85 µm or 2.0–2.7 cloacal body diameter long............................ 4

4. Body length 1.5 mm, spicules 71 μm................................................ P. albigensis Riemann, 1966

- Body length 1.39 mm, spicules 58 μm..................................................... P. faber Wieser, 1956

5. Tail conical, gubernaculum with four distal teeth....................................... P. tricuspidata Wieser, 1956

- Tail conico-cylindrical, gubernaculum plate-like without tooth............................... P. fluctispicula sp. nov.