Trombidiformes 171 



5. Gnathosoma free, not enclosed in sheath 6 



Gnathosoma enclosed in sheath formed by extension of body wall; 

 body hard; no suture between propodosoma and hysterosoma; 

 chelicerae elongated with small, equal, distal shears; with two 

 pairs of genital suckers Cryptognathidae 



6. Palpi long, turned inward; distal segment clawlike, adapted for 

 grasping; body with external plates; with two pairs of genital 

 suckers Cunaxidae 



Palpi long, elbowed, sensory organ; distal segment of palpus with 

 usually two long, sensory setae; chelicerae elongated with small, 

 equal, distal shears; body soft without surface plates; with three 

 pairs of genital suckers Bdellidae 



7. Movable chela sharp, small, for piercing; not opposed to fixed 

 chela 8 



Movable chela usually with teeth; opposed to fixed chela and 

 adapted for biting and grasping 12 



Movable chela long, whiplike, for piercing; with stylophore; 

 small mites; allied to the Tetranychidae but without thumb-claw 

 process Phytoptipalpidae 



8. With two pairs of genital suckers 9 

 Without genital suckers 10 



9. With a pair of long, fine, sensory setae on both propodosoma and 

 hysterosoma; without peritremes Ereynetidae 



With sensory setae only on propodosoma; with peritremes; with 

 small, clawlike pulvillus Paratydeidae 



10. Without peritremes, legs I normal; free-living 11 



With peritremes; chelicerae needle-like, extrusible, for piercing; 

 palpi minute, difficult to see; legs i highly specialized for grasping 

 hairs in many cases (rather heterogeneous group of genera re- 

 lated to Cheyletidae but lacking strongly developed palpi; thumb- 

 claw complex present but difficult to see because of reduction in 

 size) Myobiidae 



11. Legs with netlike armor; movable chela minute, almost invisible; 

 found in nasal passage of birds Speleognathidae 



Legs without netlike armor; movable chela large, visible; free- 

 living Tydeidae 



