ISOPOVA 373 



lamellar and functioning as gills or lungs, while the last pair, which 

 are called uropods (Fig. 602) and have a distinct exopodite and endopo- 

 dite, are elongated and function as feelers or as swimming fins: about 

 18 families and over 2,300 species, wdiich are small, creeping or swim- 

 ming animals, most of them marine, living under stones along the sea- 

 shore and among seaweed or parasitic on fish; a few live in fresh water, 

 while several very familiar species are terrestrial. 

 Key to the families of Isopoda here described : 



Oi First pair of legs chelate 1. Tanaidae 



Oa First pair of legs not chelate. 

 6i Uropods lateral. 

 Ci Uropods with telson forming a caudal fin ; pleopods mostly natatory. 



di Exopodite of uropod arches over base of telson 2. Anthurid/e 



di Exopodite of uropod does not thus arch. 

 Ci Abdomen composed of 6 segments, 

 /i Both branches of uropod well developed. 

 Qi Not parasitic ; body more or less cylindrical ; eyes usually small. 



3. ClEOLANIDAE 



gz Parasitic on fish. 

 hi Body broad and flattened ; first 3 pairs of legs prehensile. .4. .Egidae 



h^ Eyes large ; legs all prehensile 5. Cymothoidae 



/s The 2 branches of uropod not of same length, the exopodite being 



minute ; animal bores in wood 6. Limnokiidae 



Cj Abdomen composed of 2 segments 7. SPHiEROMiDAE 



Cj Uropods arch over the other pleopods, covering them 8. Idotheidae 



63 Uropods terminal. 

 Cx Animals aquatic, 

 di First antennae much smaller than the second, but not minute. 

 By Animals not parasitic. 



/i Fresh-water forms 9. Asellidae 



/j Marine forms 10. Janiridae 



d Animals parasitic on decapods 15. Bopyridae 



di First antennae minute and not easily seen 13. Ligydidae 



Cj Animals terrestrial (occasionally aquatic). 

 di Cannot roll itself into a ball (except Cylisticus convexus) . 



Ci End segment of abdomen pointed or angular 11. Oniscidae 



€2 End segment truncate or indented ... 14. TRicnoNiscroAB 

 di Can roll itself into a ball 12. Akmadillididae 



Family 1. TANAIDAE. 



Body more or. less cylindrical, with 6 free thoracic 

 segments; first pair of legs chelate ; abdominal append- 

 ages, when present, natatory; gills on the thoracic append- 

 ages: about 16 American species; marine. 



1. Tanais Audouin and Edwards. Only 3 pair of _. ^^^ 



Fig. 591 



pleopods present; uropods uniramose and short: 5 Amer- Tanais car oUni 

 ican species. 



T. cavolini Milne-Edwards (Fig. 591). Body slender, abdomen with 

 5 segments; uropods 3-jointed; length 4 mm.; width 1 mm.: Greenland 

 to Long Island Sound ; in shallow water on piles and among seaweed. 



