264 Acarology 



7. Genital organs possess more or less arched and movable genital 

 plate which through its movement opens the genital lips 8 



Genital organs without movable plates 19 



8. Many genital suckers, either small and porelike, or a few large, 

 button-like ones on genital plates or connected with these plates; 

 suckers isolated, occurring free between plates in genital lip re- 

 gion; palpal segment iv with or without clawlike or finger-like 

 projection on distal end which forms short pincers with palpal 

 segment v; frontal organ usually present; claws of legs usually 

 simple, sickle-like, and without empodium 9 



Genital suckers, usually three on each side and seldom two, four, 

 six or more, lie in a row, one after other, under or near inner edge 

 of genital plates but not connected with plates; palpal segment iv 

 without distal projection which forms shear with segment v; 

 frontal organ lacking, with few exceptions; tarsal claws often 

 double-pronged and with empodium 12 



9. Palpal segment iv usually with robust spine or conelike appendage 

 on distal end which is not equal in length to palpal segment v and 

 does not form pincer; paired lateral eyes rarely found close to- 

 gether in sclerotic plate 10 



Palpal segment iv with narrow, finger-like projection on its distal 

 end which opposes ultimate segment and forms shear with it; lat- 

 eral eyes not in capsules, separated from each other; frontal organ 

 not present; body skin weak and without sclerotic plates 



Hydrodromidae 



10. Legs without true swimming hairs 1 1 

 Legs with swimming hairs; body usually soft-skinned and usually 

 with sclerotic plate on anterior portion; seldom many plates 



Hydryphantidae 



11. Body covered with beautifully designed radiating sclerotic plates; 



with many genital suckers Clathrosperchonidae 



Body simply armored; with many genital suckers; living in hot 

 springs Thermacaridae 



Body without armor but with skin papillae; with three pairs of 

 large genital suckers Ctenothyasidae 



12. Palpal segments iv and v not dorso-ventrally flat and shovel-like 13 



Palpal segments iv and v medio-laterally broadened and dorso- 

 ventrally strongly flattened, and with four medio-laterally end 

 claws of segment v forming shovel-like organ Rutripalpidae 



