Trombidiformes 199 



4. Caenonychus Oudemsins, 1903 



Type. Caenonychus fallcLx Oudemans, 1903 



Discussion: There are only a few described species, but the distri- 

 bution is probably world-wide and these mites have been overlooked 

 because of their minute size. They are usually to be found in moss and 

 soil and it has been stated that Nanorchestes amphibius Topsent and 

 Trouessart is practically marine in habit. They are probably preda- 

 ceous. 



One species, Nanorchestes pulvinar Grandjean, presents an inter- 

 esting arrangement in the forward pair of propodosomal sensory setae. 

 The long "sense setae" activate a short seta which apparently is the 

 true sensory organ. 



Grandjean 1942 lists the stages of Nanorchestes as larva, three 

 nymphal, and adult. The males are differentiated from the females 

 by the larger number and position of the genital setae. 



A Speleorchestes sp. from Mexico possesses a tracheal system open- 

 ing at the base of the chelicerae. 



References: 



Grandjean, F. 1942. Observations sur les Acariens (7 Ser.). Bull. Paris 



Mus. d'Hist. Nat. Ser. 2, 14(4) :264-267. 

 Womersley, H. 1944. Australian Acarina, families Alycidae and Nanorr 



chestidae. Trans. Roy. Soc. South Austral. 68(1) :133-143. 



Pachygnathidae Kramer, 1877 



Figures 142-144 



Diagnosis: These are small, whitish mites ranging from 0.30 to 0.40 

 mm. in length. The skin is soft and may be striate, reticulate, or with 

 diverse pattern. The pachygnathids possess an anterior protuberance 

 or tectum which varies in shape. They have no median eye and may 

 or may not have lateral eyes. The propodosoma is separated from the 

 hysterosoma by a suture and has two pairs of sensory setae (in Pe- 

 tralycus the anterior pair is globose while in Bimichaelia the posterior 

 pair is globose). The hysterosoma may or may not be segmented. The 

 chelae of the chelicerae are opposed and the palpus is five-segmented 

 without the claw-thumb complex. The legs are in two distinct groups. 

 All tarsi are provided with two claws and a pulvillus (the claws are 

 simple and the pulvillus rayed); in Petralycus femora i, ii and iii are 



