270 



Acarology 



projects well beyond the anterior margin of the body but in a few 

 forms is completely hidden in the dorsal view The palpi have three 

 or four segments which are attached laterally, dorso-laterally. or dor- 

 sally to the base of the capitulum. The maxillary portions of the palpi 

 are completely fused. Lying in a dorsal groove in the rostrum the che- 

 licerae are retractile; the ventral digit is large and movable while the 

 dorsal digit is reduced to a pointed membrane. The tracheal system is 

 very rudimentary and quite certainly is not functional in respiration. 



Figure 185 Halacarus {Thalassarach- 

 na) subterraneus (Schuiz). Dorsum of 

 male. (After Newell 1947) 



Figure 186 Copidognathus {Arhodeo- 

 poms) siibmarinus Newell (left), pal- 

 pus of female; Halacarus {Thalas- 

 sarachna) cap/yzmw^ Lohmann (right), 

 chelicera of female. (After Newell 

 1947) 



Usually four plates dorsally (predorsal, postdorsal, and right and left 

 ocular plates) and four plates ventrally and laterally (anterior epimeral, 

 right and left posterior epimeral, genito-anal plates) reinforce the cuti- 

 cle of the body wall. These plates show varying degrees of subdivisions 

 or fusion in different genera, in different species of a single genus, or 

 rarely in the two sexes of a single species. The legs are attached later- 

 ally: legs I and ii are borne on anterior epimeral plate (or plates), and 

 project anteriorly; legs in and iv are borne on the right and left pos- 

 terior epimeral plates and project posteriorly. In adults the legs have 

 six segments. The larvae have only three pairs of five-segmented legs. 

 Leg IV in the protonymph is also five-segmented but legs i, ii, and iii 

 are six-segmented. All legs in the deutonymph are six-segmented. The 

 tarsus always has two lateral claws while a median claw may be pres- 

 ent or absent. The salivary glands are well developed. The mid-gut does 



