NO. 7 PROTECTIVE ADAPTATIONS — McATEE 21 



are eaten by fishes as well as by birds. Cladoccra and Copepoda are 

 eaten freely by larval salamanders and to a lesser extent by recently 

 transformed frogs. They and all other small fresh-water crustaceans 

 fall a prey to Hydra and aquatic insects. vSmall marine forms are 

 engulfed even by protozoans. Barnacles are eaten by the tautog, and 

 by sea-anemones and sea-urchins. More than 80 kinds of Crustacea 

 have been identified from stomachs of haddock taken in waters about 

 Scotland (Thomas Scott). Crustacea have parasites from among 

 their own ranks, and from among the worms. 



Discussion. — Most of the small Crustacea are translucent or trans- 

 parent but this does not save them from their foes. Practically all 

 aquatic animals " get their start " by feeding on these Crustacea, the 

 list including a great variety of insects, fishes, and batrachians. Many 

 of them continue feeding upon Crustacea when adult, and so com- 

 mon is this habit that in many cases small Crustacea are the animal 

 basis of the food for the entire fauna of certain waters. This is true 

 of the Artemia of Great Salt Lake, previously discussed, and con- 

 spicuously so of the Mysidacea, Amphipoda, Isopoda, Euphasiacea 

 and Macrura of northern oceans, where everything from other 

 Crustacea, through fishes and birds up to whales preys incessantly upon 

 them. There is no question of special protection here but solely of 

 numbers and fecundity. 



The protection that Crustacea might be supposed to derive from their 

 more or less indurated exoskeleton is discounted by the fact that in 

 most cases there are plenty of enemies large enough to swallow them 

 whole. Of what avail for instance is the bivalved shell of the almost 

 microscopic Ostracoda? The same principle applies all along the line 

 up to and including the crabs, for most crab-eaters swallow their 

 prey entire ; however there are some crabs that grow so large they are 

 possibly almost free from enemies when adult. 



The claws of the large decapods naturally are of little avail against 

 enemies so voracious as to swallow the crustaceans whole and there 

 is no evidence known to the writer that the self -mutilation practiced 

 by decapods results in enemies swallowing the claw and letting its 

 owner escape. 



Birds find the Hippidae or sandbugs, despite their burrowing habits, 

 and hermit crabs, adopted shell and all, are freely eaten by birds and 

 fishes. In numerous cases the hermit crabs found in bird stomachs 

 were those with hydroids and bryozoa growing on their carapaces 

 or shelters. Why should it even be supposed that such combinations 

 of animals are protective when the enemies of one of them are in 

 most cases enemies of all? For instance the diving ducks and fishes 



