THE CRAYFISH AND OTHER CRUSTACEA QI 



remains protected within the deeper part of the shell has 

 become soft and fleshy. The terminal appendages of the 

 abdomen have been modified into organs to enable the 

 crab to retain its hold of the shell. In front of these the 

 appendages are generally absent on the right side of the 

 abdomen, an indirect consequence, probably, of the spiral 

 twist to which the abdomen is subjected. In the males 

 the terminal appendages of the ab- 

 domen are often the only ones 

 present. Hermits hang on to their 

 shells with great tenacity and may 

 even allow their bodies to be torn 

 in two before releasing their hold. 

 When the hermits outgrow their 

 shells they hunt larger ones and a 

 hermit often tries to take possession 

 of a shell that is occupied by 

 another individual. 



The true crabs usually have a 

 short, broad carapace and a small 

 abdomen which is folded under the 

 cephalothorax where it fits neatly 

 into a concave space. The crabs 



. FIG. 75. The common 



which are best known are those shrimp, Crangon vuiga- 

 prized for food, such as the blue rts ' 

 swimming crab of the Atlantic coast; but there are many 

 species which have very interesting habits. Among 

 these may be mentioned the fiddler crabs, the males 

 of which have an enormously developed cheliped which 

 is held horizontally across the front of the body. These 

 active creatures live in holes dug in the sand or mud near 

 the water's edge. They run with a good deal of agility 

 and usually make for their holes at the appearance of 



