378 NORTH AMERICAN FAUNA 61, FISH AND WILDLIFE SERVICE 



Orchcstia traskiana was the most commonly observed species 

 living under the shelter of stranded seaweed or rocks through- 

 out the Aleutians. The principal food of this crustacean 

 seems to be decaying seaweed, of which there is a limitless sup- 

 ply; it also eats decaying fish, shellfish, sea birds, and mammals 

 cast up from the sea. Orchestia is often found associated with 

 the isopod Lygia pallasi and carabid beetles. 



Beach fleas are of more than passing interest for, in spite of 

 their small size, they may form the major item of food for the 

 blue fox. As a general rule, on islands where sea birds are plenti- 

 ful the fox droppings contain mostly feathers and few or no beach 

 fleas. Where birds are not available, however, the droppings are 

 characteristically whitish in color and are composed of the 

 chitinous exoskeletons of beach fleas and isopods, together with 

 traces of other beach organisms. 



Paracyamus boopis (fig. 8) occurs on the skin of the humpback 



Figure 8. — Parasitic amphipod, Paracyamus boopis, from skin of humpback 

 whale. Akutan Island, August 6, 1938. 



