42 



Acarology 



the dorsal surface of the apex, but no pitUke Haller's organ, such as 

 is found in the ticks, is present. (Haariov 1943). 



The idiosoma is armored with sclerotized plates. On the dorsal sur- 

 face there is usually a single plate, but this may be completely or par- 

 tially divided into two or more plates. Laterally there may be plates 

 that connect the dorsal plate to the ventral plates, or lateral plates may 

 be entirely lacking in which case soft, striated integument connects 

 dorsal and ventral sclerites. 



Tritosternum 

 Prestemal Seta 

 Praeendopodal Plate 

 Jugular Plate 

 Peritremal Plate 

 Para pedal Plate 

 Endopodal Plate 

 Sternal Plate 

 Metasternal Plate 

 Lateral Plate 

 Epigynial Plate 

 Metapodal Plate 

 Ventral Plate 



Anal Plate 



Figure 34 A diagrammatic arrangement of the ventral plates that may be 

 encountered in the Mesostigmata. A median plate, if present, will have the same 

 position as the epigynial plate. 



The ventral plates are of extreme importance in recognizing the 

 suborders (Figure 34). Just posterior to the gnathosoma in the mid- 

 line there is the tritosternum. The tritosternum consists of a basal por- 

 tion and two or three setiform distal processes. The tritosternum is a 

 modified remnant of the sternal plates of the third segment and is the 

 only relic of the primary stemites. Flanking the tritosternum there may 

 be a pair of presternal setae and or praeendopodal plates that always 

 lack setae. These plates are called jugular plates by Ewing 1928, but 

 Tragardh reserves the term jugular for plates anterior to the sternal 

 plate that bear sternal setae and may or may not have pores. Posterior 

 to the tritosternum lies the so-called sternal plate. In some genera this 

 plate bears four pairs of setae and three pairs of pores. The sternal 

 plate is thought to have been formed by the fusion of coxal plates with 

 the ventral body wall. The presence of four pairs of setae on some 



