Key to species of the Sperchon tridentatus -group

1 Integument without muscle attachment sclerites............................................................. 2

- Integument with muscle attachment sclerites............................................................... 3

2 P-4 shorter than P-3, P-2 distoventral projection bearing three fine setae, P-3 ventral margin straight (Fig. 22), claw lamella with straight ventral margin (Fig. 23), excretory pore unsclerotized (Sokolow 1940).......................... S. tridentatus

- P-4 longer than P-3, P-2 with thick seta near base of distoventral projection which bearing two fine setae (Fig. 19), P-3 ventral margin convex, claw lamella with concave ventral margin (Fig. 21), excretory pore sclerotized (Fig. 16)...... S. smiti sp.n.

3 All dorsocentral sclerites free and sclerotized (Fig. 1), P-2 with rather long ventrodistal projection bearing two fine setae (Fig. 7), all genital acetabula subequal in size and distinctly separated (Fig. 3), excretory pore (Fig. 2) unsclerotized.................................................................................................... S. pesici sp. n.

- Dorsocentral sclerites dc.1 and dc.2 unsclerotized, dc.3 fused with glandulartia Sci (Fig. 24), P-2 distoventral projecting short and without fine setae, with single thick seta near base of projection (Fig. 26), ac.2 larger than ac.1 and ac.3, all acetabula slightly separated, excretory pore (Fig. 25) sclerotized (Tuzovskij 2003)................................... S. minor