CHAPTER VIII 



Orihatei Duges, 1833 



THE gnathosoma is usually concealed within a camerostome. 

 Stigma and tracheae may be present, opening into porose areas. 

 Pseudostigmatic organs are generally present on the propodosoma. 

 The body is usually strongly sclerotized, dark in color, and when not 

 thusly armored the skin is leathery. The coxal apodemes are sunk be- 

 neath the skin but are still visible, although not as strongly so as in the 

 Acaridiae. The tarsi have one to three claws and are without carun- 

 cles. The palpi usually have five movable segments. The two sexes are 

 similar. Three pairs of genital suckers are present; the males do not 

 possess adanal suckers; and both sexes generally have the genital and 

 anal openings covered by lidlike shields. 



The Oribatei, although divided into many larger groups by Euro- 

 pean workers, can be easily separated into two distinct groups — the 

 Aptyctima and the Ptyctima — in that in the former the propodosoma 

 is not movably hinged with the hysterosoma, whereas it is hinged in 

 the latter group. 



Within the Aptyctima we find several natural groups based on the 

 genital-anal plate arrangement, and possession or lack of pteromorphs 

 or wings. Because of the complexity and uncertainty of these divisions 

 the reader is referred to Vitzthum, Willmann, and Sellnick. A rather 

 comprehensive study of these mites^ as a whole will have to be made 

 before these characters can be properly weighed and evaluated. 



The oribatid mites, once considered as of taxonomic interest only, 

 have gained economic importance owing to the discovery that many 

 of them have been found to be hosts of various tapeworms. In studies 

 of soil fauna there is an indication that these mites, which constitute a 

 high percentage of the fauna, are important factors in promoting soil 

 •fertility through breaking down organic matter by digestion, as do the 



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