Key to the four species of Archeterokrohnia

1 Tail section ~50% total length, lateral fins beginning halfway between trunk-tail septum and ventral ganglion, ventral ganglion centered 2/3 distance from head to trunk-tail septum, corona ciliata shaped like an outside caliper, fins rayless........................................................................................... A. rubra Casanova, 1986 a

- Tail section ~55% of total length, lateral fins with rays and beginning at or near trunk-tail septum..................... 2

2 Head trapezoidal, anterior teeth replaced with plates bearing denticles, pair of palps with teeth-like processes located below vestibular organ................................................................ A. palpifera Casanova, 1986 b

- Head triangular, both anterior and posterior teeth, well-developed vestibular organs................................. 3

3 Total length 12.9 mm, 6–8 anterior teeth, 1 posterior tooth, no vestibular plates or palps, head with apical gland-cell complex, triangular process on head absent.......................................... A. longicaudata (Hagen & Kapp, 1986)

- Total length 28.5 mm, 10–11 anterior teeth, 4 posterior teeth clustered below a vestibular plate bearing denticles, ventral ganglion slightly posterior to midpoint between head and trunk-tail septum, anterior of head with a triangular process............................................................................................. A. docrickettsae n. sp.