CHAPTER V 



M 



The Suborder Tromhidiformes Renter^ 1909 



THESE mites possess a pair of stigmata on or near the gnathosoma, 

 although occasionally the stigmata may be absent. The palpi are 

 usually free and highly developed, either as pincer-like clasping organs 

 or sensory organs. The chelicerae are usually modified for piercing, 

 although in the primitive, predaceous families a few have opposed 

 chelae which are apparently for seizing prey. They may or may not 

 possess genital suckers, but anal suckers are never present. 



The Tromhidiformes are here divided into three groups, the Tetra- 

 podili, the Tarsonemini, and the Prostigmata. The Tetrapodili contains 

 the tiny, wormlike, plant-feeding Eriophyidae which possess only two 

 pairs of legs in all stages and which lack a respiratory system. The 

 Tarsonemini includes the small plant and arthropod parasites with 

 minute mouth parts, small appressed palps, tiny needle-like chelic- 

 erae, and with the stigma behind the pedipalps in the female and 

 lacking in the male; many in this group do not possess the full number 

 of legs and appear to be quite degenerate. The Prostigmata is com- 

 posed of those mites with the stigma opening at the base of the che- 

 licerae; they are usually large mites with large, free-moving mouth 

 parts, in many cases the palps being highly developed as feelers or 

 grasping organs. The chelicerae, although perhaps modified, usually 

 are large and well developed for piercing or grasping. In the Tarso- 

 nemini we have a single more or less homogeneous group, but in the 

 Prostigmata we find many groups, such as those with a thumb-claw 

 complex on the palps (Trombidiidae), those with very simple palps 

 (Rhagidiidae), those with piercing, needle-like chelicerae (Tetrany- 

 chidae), or those with grasping or crushing mouth parts (Rhagi- 

 diidae). These, with their related families, perhaps form the basis for 



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