Introduction 



17 



seta that is probably a chemo-receptor. They are called "solenidien" 

 by Vitzthum and "solenidions" by Grandjean. They are hollow and a 

 living extension of the cells associated with them fills their lumen. They 

 are directly connected with the peripheral nervous system. They are 

 most commonly found on the distal segments of the appendages. 



,/% 



Figure 10 Types of body setae found on various mites. Top row; simple, pilose 

 [Neocheyletiella rohweri Baker, 1949], plumose [Eiischongastia peromysci 

 (Ewing), 1929], capitate [Spathulathrombiimi soiithcotti ( Womersley ) , 1935]; 

 middle row: spatulate, cordate [Spathiilathromhium maximum Womersley, 

 1945], palmate [Cheletogenes oniatiis (Canestrini and Fanzago, 1876)], pilidi- 

 form [Holcotrombidium securigeriim (Canestrini), 1897]; bottom row: furcate 

 [Hiotrombidiiim tubhi (Womersley), 1937], chambered [Camerotrombidium 

 opulentiim (Womersley), 1945], and dentate [Acaropsis docta (Berlese), 1886]. 



In addition to the striated sensory setae, microsensory setae ("fam- 

 ulus" of Grandjean 1935), are regularly found on the genu, tibia, and 

 tarsi of the legs. Their function is not known but it is unlikely that such 

 small structures would be tactile in nature. Whiplike setae ("acan- 

 thoides" of Grandjean 1935), are ,also common on the legs. They 

 differ from ordinary setae in being longer and nude. These setae might 

 function as tactile organs. 



Certain setae are frequently associated with particular structures. 

 Sensillae are setiform organs that arise from specialized pits, pseudo- 

 stigmata, or sensillae bases, usually found on the propodosoma. The 

 sensillae may be of almost any form but almost invariably they are 

 readily distinguishable from the body setae. A specialized forked seta 

 is found on the palpal tarsus of most of the IVTesostigmata. 



