CKUSTACEA 



287 



General. Crustacean problems parallel those of the mol- 

 lusca. Lobsters, crabs, shrimps, and crawfish are valuable for 

 food. Some of the most highly prized species require to be pro- 

 tected by law, and we are beginning to work out methods for 

 their artificial propagation. Some of the terrestrial crawfish 

 are locally injurious to vegetation. There is this difference : 

 crabs and lobsters move about more freely than clams and 

 oysters, and hence are not so well suited to stable aquicul- 

 ture. On this account the United States Bureau of Fisheries, 

 and the fish commissions of the states concerned, must assume 

 responsibility for keeping up the supply by propagation, since 

 this cannot be done with profit by private individuals. 



Economic value. The table below presents the chief eco- 

 nomic Crustacea, and its most suggestive feature is likely to 

 be the wide difference between actual and possible utilization 

 of these resources. 



CRUSTACEAN PRODUCTS OF THE UNITED STATES IN 1008 



Classification. The Crustacea are divided into two main 

 groups, the Entomostraca (mostly microscopic or small, includ- 

 ing the ostracods, copepods, and barnacles) and the Malacos- 

 traca (the lobsters, crawfish, shrimps, prawns, and crabs). 



Entomostraca. Although inconspicuous and little known, 

 these minute Crustacea are of the greatest biological signifi- 

 cance. If we had them all gathered into a ball, and all the 

 rest of the animal matter of the world rolled into another 



1 Estimates not obtainable. 



