246 Acarology 



orly the scutum ends in an expanded plate that may project over 

 the gnathosoma as a tectum. This plate bears numerous setae, or 

 the plate may be lacking and the scutum rudimentary, consisting of 

 little more than areas for the origin of the sensillae. One subfamily 

 (Stygothrombiinae) is extremely degenerate and lacks numerous 

 setae, and typical mouth parts, and its body shape is long and worm- 

 like. 



Larval trombidiids have a single urstigmen associated with leg i, 

 usually more than one dorsal plate, and the seta on the pedipalpal 

 coxa is usually anterior to the base of the palpal femur. These mites 

 are parasitic on invertebrates. 



Thor and Willmann 1947 have divided the family into fifteen sub- 

 families. One of these subfamilies, the Trombiculinae, is now recog- 

 nized as a family and will be considered in the next section. A key to 

 the subfamilies, based on adults, modified from Thor and Willmann, 

 follows: 



Key to the Trombidiidae 



1. Propodosoma with crista enclosed in plates of various shapes or 

 free in integument 2 



Propodosoma without crista; scutum rudimentary; sensillae at- 

 tenuate and nude Trombellinae 



2. One pair of sensillae 4 

 Two pairs of sensillae 3 



3. Three hysterosomal plates Notothrombiinae 

 Hysterosomal plates lacking Johnstonianinae 



4. Sensillae arising from sensillary area 6 

 Sensillae not arising from sensillary area 5 



5. Scutum expanded Calothrombiinae 

 Scutum straight Tanaupodinae 



6. Peritreme associated with cheliceral stigmata; eyes on movable 

 peduncles 7 



No peritreme present; eye if present not on movable peduncle 8 



7. Pulvillus present between ambulacral claws AUothrombiinae 

 Pulvillus absent Trombidiinae 



