194 ANIMALS WITH JOINTED LEGS— THE ARTHROPODS 



an enlarged salt-water edition of the crayfish, and the body organs and 

 habits are very similar in the two. 



The crabs are also crustaceans and have appendages of the cephalo- 

 thorax very much like the crayfish, but the abdomen is greatly reduced 

 and folded up under the cephalothorax. There are many varieties of 

 crabs. The edible or blue crab is an important source of food in the 

 United States. Unlike the lobster, the main muscles consumed as food 

 are located in the cephalothorax and are used to control the powerful 

 pinchers. The fiddler crab has one pincher larger than the other in the 

 males and the two are held in a position somewhat like a bow and 

 "fiddle." The hermit crab backs up inside a deserted mollusk shell, 

 usually of the coiled gastropod type, and carries it around on his back. 

 The body is soft and can curve around inside the shell. The little sand 

 crabs come out on the sand of the beach and can run very fast over loose 

 sand, traveling sideways for better traction. They are so common on 

 some beaches that a sun bather stretching out on the sand must be care- 

 ful or he might receive a pinch which informs him of the sand crab be- 

 neath him. 



Shrimp cocktails as a dinner appetizer have become standard fare in 

 all parts of the United States. The catching and shipping of these 

 shrimp constitute a major industry in certain coastal regions, especially 

 in southern Louisiana. The industry in this region was stimulated re- 

 cently when very large shrimp were discovered in the Gulf of Mexico. 

 It seems that the shrimp that we ordinarily eat are not fully grown, but 

 they mature sexually and reproduce in this small size and then retire 

 into the Gulf and congregate in large schools. Here they grow nine and 

 ten inches long. 



The fairy shrimp are very beautiful little crustaceans often found in 

 great numbers in small temporary ponds in the spring. They swim on 

 their backs by undulating movements of the appendages, making a beau- 

 tiful sight. They possibly get their name from the fact that they seem 

 to have the power to make themselves disappear in the summer when 

 the ponds dry up and reappear in the following spring. The adults actu- 

 ally die when the ponds dry in the spring, but the previously laid eggs 

 live through the dry summer and are ready to hatch when the rains and 

 warmth of spring return. 



Barnacles are crustaceans that bear a superficial resemblance to mol- 

 lusks. They have developed a shell and become permanently attached 

 to some solid support as adults. The young are free-swimming, but 

 soon pick a rock, wharf, ship bottom or similar underwater structure for 

 attachment. They are a great nuisance to shipping since ships often 

 have to be hauled into drydock to have the barnacles scraped from them. 



