CiiLSTACEA 



28' 



General. Crustacean piohk'ins parallel those of tlio mol- 

 lusca. Lobsters, crabs, shrimps, and crawlish arc valual)i(' lor 

 food. Some of the most hiLrhly prized species rccjuirc to Itc pro- 

 tected by law, and \\v are be<»inninf( to work out melliods for 

 their artilieial propagation. Some of the terrestrial ci-awfish 

 are locally injurious to vegetation. There is this diiVerenee: 

 crabs and lobsters move about more freelv than elams and 

 oysters, and hence are not so well suitecl to stable acpiiciil- 

 ture. On this accotmt the United States Hureau of Fisjieries, 

 and the lish connnissions of the states concerne(l, must assume 

 responsibility for keeping up the supply by propagation, since 

 this cannot be done with protit by private individnals. 



Economic value. The table below presents the ehief eco- 

 nomic Crustacea, and its most suggestive feattire is likelv to 

 be the wide difference between actual and possible utilization 

 of these resources. 



CkCSTACKAN rUolUCTS <»F THK fNITKO StATKS IX ll>OS 



Lobsters . . . 

 Blue crabs . . 

 Shrimps, prawns 

 I'acitic crabs . 

 Crawlish . . . 



ACTCAL VALI E 



^1,031,000 



012.000 



404.000 



1 -J 7.000 



82,000 



Pt)SSIBLK VALCE' 



Classification. The Crustacea an^ (livide(l into two main 

 groups, the Entomostraca ( inostly microscopic or small, iiiclnd- 

 ing the ostracods, co[)epods, and barnacles) and the Muldms- 

 tracn (the lobsters, crawlish, shrimps, prawns, and crabs). 



Entomostraca. Although inconspicuous and little known, 

 these minute Crustacea are of the L-reatest biolotxical si^jniti- 

 cance. If we had them all gatluM-ed into a ball, and all the 

 rest f)f the animal matter of the world rolled into another 



^ Kstiinates not obtainable 



