Mesostigmata 41 



work much information concerning the Gamasides is needed before a 

 satisfactory understanding of that group will be achieved. Of the 1,290 

 species reported by Vitzthum 1939, 889 or more than 75 per cent 

 belonged to the Gamasides. 



Tragardh follows the more commonly accepted classification of the 

 Acarina and assigns the Mesostigmata to the rank of supercohort. In 

 the present discussion Tragardh's supercohort will be considered a 

 suborder. Tragardh's classification will be followed in spirit except 

 that the names of the categories and some of his subdivisions will be 

 omitted. 



Morphology: Mesostigmatid mites are usually well armored with 

 brown to deep brown sclerotized plates or shields. In almost every case 

 {Rhodacarus is an exception) the body consists of two distinct re- 

 gions: an anterior, minute gnathosoma and a posterior idiosoma. In 

 the Uropodina, one of the groups, the gnathosoma is frequently en- 

 closed in a cavity (camerostome) in the idiosoma. 



With a little experience the general facies of mesostigmatid mites 

 will enable the student to recognize more than 90 per cent of the spe- 

 cies. However, all species that have either a tritosternum or one pair 

 of lateral stigmata with a sinuate peritreme or both may be safely 

 placed in the Mesostigmata. Of particular importance in the classifica- 

 tion of the suborder is the distribution of the ventral plates, ventral 

 setae, and ventral pores. Since Tragardh's classification is to be used 

 his nomenclature for the structures will be used where applicable. 



The gnathosoma of mesostigmatid mites is a complicated apparatus. 

 The chelicerae and the distal segments of the pedipalps are relatively 

 unmodified, but the fused basal segments of the pedipalps that form 

 the ventral wall are extended anteriorly and dorsally as several projec- 

 tions and sheaths about the chelicerae. Dorsally an anterior projection 

 extends over the gnathosoma and is called a tectum by Snodgrass 1948 

 or epistome by other authors. In the. midline of the gnathosoma there 

 is usually a groove that has markings reminiscent of recurved teeth. 

 Lateral to the gnathosomal groove are the two main sections of the 

 ventral wall of the gnathosoma. Anteriorly these are differentiated into 

 a median hypostome, lateral cornua, and more medial paralabra. 



The legs of the mesostigmatids are usually well sclerotized. They 

 typically have six or seven movable segments. The tarsi end in pre- 

 tarsi that usually bear sucker-like caruncles and a pair of ambulacral 

 claws. Tarsus i is frequently provided with a tuft of sensory setae on 



