20 



Acarology 



tectum is an anterior projection. It consists of a thin, chitinous plate 

 that is usually toothed at its free end (Figure 13 ). The tectum may be 

 so reduced in some mites as to be entirely lacking. 



The chelicerae originate below the tectum although they are at times 

 covered by dorsal extensions of the pedipalps. These organs are so 

 important that they will be considered later under a separate section. 



Figure 13 Tecta of various mites. Upper row, from left to right, Pergamasus 

 olivaceus Vitzthum, 1927; Discopoma regia Vitzthum, 1921; Neopodocinum 

 coprophiliim Vitzthum, 1926: lower row Trigonholaspis salti Vitzthum, 1930; 

 Cyrtolaelaps capreolus Berlese, 1904. (After Vitzthum 1.940) 



Between and below the chelicerae is the mouth. The mouth is ven- 

 tral to the labrum and dorsal to the hypostome. These structures may 

 be elaborately developed, but they are seldom seen because their pres- 

 ence is overshadowed by the pedipalps and chelicerae. Laterally the 

 oral opening may be flanked by paralabra which may assist in closing 

 the mouth and probably aid in directing food into the opening. In the 

 Notostigmata and the Holothyroidea a toothed, radula-like organ de- 

 rived from the labrum is associated with the oral opening. 



The pedipalps form the lateral-ventral surface of the gnathosoma. 

 In some groups the basal expansions of the pedipalps extend medially 

 and dorsally and fuse in the midline to form a tube in which the che- 

 licerae are found. 



The hypostome forms the ventral-median wall of the gnathosoma. 

 In most groups it is insensibly fused with the pedipalps but in the ticks 



