DECAPOD CRUSTACEA. 



165 



taken upon tne shores of New England and Canada amounts 

 to oetween twenty and thirty 

 million annually. Crayfish 

 are used largely as food in 

 Europe, and are bred in ponds 

 for the market, but in Amer- 

 ica they are largely neglected. 

 Shrimps and prawns are 

 largely salt-water forms, but 

 some of the prawns occur in 

 fresh water in the warmer 

 parts of the world. The line 

 between the two is not easily 

 drawn except by saying that 

 the body of the shrimp 

 is flattened (depressed) from 

 above downwards, while that 

 of the prawn is compressed 

 (flattened from side to side). 

 In America, " shrimp salad " 

 is almost universally made 

 from prawns. 



Of the Anomura, the most 

 interesting are the so-called 

 hermit-crabs. These are somewhat lobster-like, but the 

 abdomen is but slightly hardened, and so, to protect this 

 vulnerable part of the body, the crab inserts it in a deserted 

 snail-shell, and this "house" he carries about with him 

 wherever he goes, retreating into it and closing the opening 

 at the approach of danger with his solid pincing-claws. 

 With increase in size the crab must move into a larger 

 shell. In other Anomura the back is. soft, and these 



FIG. 74. Common shrimp (Crangon 

 vulgaris). From Emerton. 



