Hydrachnellae 263 



well-defined sutures; anal opening in large plate; epimera i not 

 forming tube Hydrovolziidae 



Legs II and iv arranged so epimera not seen from above; epimera 

 not separated by suture; anal opening in small plate; epimera i 

 closes together anteriorly to form tube Rhynchohydracaridae 



3. Rostrum not elongate or awl-like, but conelike or other form and 

 essentially shorter than palpus; chelicerae definitely two-segmented 

 and with sickle-like cheliceral claw and basal segment 4 

 Rostrum long, narrow, awl-like, more or less pointing ventrally 

 and reaching about to tip of palpus; chelicerae, on the whole, 

 slightly curved and stylet-like, the cheliceral claw and basal seg- 

 ment not noticeably separated; chelicerae with posterior end reach- 

 ing far into interior of body Hydrachnidae 



4. Genital organ without valvelike flaps or plates but with ledgelike 

 or clasplike sclerotic structure surrounding genital suckers; genital 

 suckers fastened in soft body skin, very small or more or less 

 stalked and posteriorly often acorn-like 5 

 Genital organs with valvelike or platelike sclerotic sections, on or 

 under which are more or less distinct genital suckers (exception: 



a Fiona species with dispersed, disklike suckers on ventral skin) 7 



5. Double eyes either located medianly on ends of transverse scle- 

 rotic shield to form so-called spectacle or lie laterally either in 

 shields or free in skin; palpi of normal size and much longer than 

 rostrum 6 

 Double eyes located laterally on more or less rodlike longitudinal 

 sclerotic shield; palpi very small, only weakly surpassing rostrum; 



all legs richly haired but without true swimming hairs; body so 

 soft that mite collapses when removed from water Limnocharidae 



6. Double eyes lie medianly and are bound together by single trans- 

 verse plates, or are lateral and are bound together by many-seg- 

 mented plate; no true rostrum present but with large sucking 

 mouth surrounded by "ruffles"; palpal segment iii with group of 

 setae on distal end; in the mites with-^eyes bound together by trans- 

 verse plate genital suckers tiny and distributed over entire body 

 skin; whereas in other group suckers are large and lie in shields on 

 each side of genital opening Eylaidae 

 Double eyes lie laterally, free in the body skin, without sclerotic 

 plate connecting them; rostrum present; mouth opening not 

 sucker-like and without "ruffles"; no group of setae on distal end 



of palpal segment in; genital suckers often stalked and acorn-like 



Protziidae 



