14 ISOPODA 



Key to suborders of Isopoda 



1. Parasitic on crustaceans; body of 9 nearly always asymmetrical 



Epicaridea 



Free-living or parasitic on fishes; body of 9 bilaterally symmetrical, or 

 if parasitic, 9 somewhat distorted 2 



2. Body more or less bilaterally compressed Phreatocoidea* 



Body more or less dorsoventrally depressed or subcylindrical 3 



3. With six pereonites and five pairs of pereopods Gnathiidea 



With seven pereonites and six or seven pairs of pereopods 4 



4. Body usually more than six times longer than wide, subcylindrical, 



uropods never operculiform 5 



Body usually less than six times longer than wide, usually 



dorsoventrally depressed; if subcylindrical, uropods operculiform . . 6 



5. Uropodal exopod often folding dorsally over pleotelson; rarely 



interstitial forms Anthuridea IjlC 



Uropods terminal, exopod lacking; minute interstitial forms 



Microcerberidea 



6. Antennules minute; terrestrial forms, with pleopods tracheate 



Oniscidea 



Antennules rarely minute; aquatic forms, pleopods never tracheate . . 7 



7. Uropods ventral, operculiform, covering pleopods Valvifera 9' 



Uropods never operculiform over pleopods 8 



8. Uropods lateral or ventrolateral, forming tailfan with pleotelson; 



pleopods 1 and 2 rarely operculiform Flabellifera^ IK 



Uropods terminal or subterminal; pleopods 1 and 2 variously 



operculiform Asellota ? 7^3 



* The suborder Phreatocoidea contains freshwater forms, and has a 

 Gondwanian distribution, primarily in the Southern Hemisphere. 



Pleopods (on pleonites 1-5) biramous, lamellar, primarily for respiration; 

 anterior pleopods occasionally operculiform. Pleopod 2 in male (and occa- 



