PHYLUM ARTHROPODA — CLASS CRUSTACEA 281 



shed the outer cuticle. This is repeated seven or eight times during 

 the first season to allow for growth. The average life span of the 

 crayfish that reaches maturity is about four years. 



Regeneration and Autotomy 



This power is limited to the appendages and eyes in this animal, 

 but it is quite well developed in these parts. The possibilities and 

 rate of regeneration are greater in younger animals. Mutilated or 

 lost legs or mouth parts are readily restored. 



The genus Cambarus has the ability to allow a walking leg to 

 break off at a certain line or joint if it is caught or injured. A new 

 leg will develop from tliis stump. This phenomenon is called autot- 

 omy. There are special muscles to help in this and a membranous 

 valve stops the passage of blood through the leg, thus preventing ex- 

 cessive bleeding. Bleeding will stop more quickly if the break oc- 

 curs at such a point than it would otherwise. Autotomy often 

 makes it possible for the animal to sacrifice a leg to save its life. 



Economic Relations 



Crayfish and the entire class Crustacea are of considerable im- 

 portance to man. The crayfish, lobster, crab, shrimp, and others 

 are used directly as food to the extent that it is an industry valued 

 at several million dollars annually in the United States. The 

 numerous smaller genera, like Daphnia, Cyclops, Cypris, Gam- 

 marus, Asellus, and Euhranchipus, comprise a large part of the food 

 of many of our food fish either directly or indirectly. The more 

 minute ones also feed many clams and oysters and finally end in 

 human consumption. The shrimp and crab fisheries are the most 

 important of the Crustacea on the Texas coast of the Gulf of Mexico. 

 In the Mississippi valley and on the Pacific Coast the crayfish is 

 used extensively as a food. It becomes a serious pest in the cotton 

 and corn fields of Louisiana, East Texas, Mississippi, and Alabama, 

 They fill the swampy land with their burrows where they come up 

 to the surface and eat the young plants. Frequently their burrows 

 do serious damage to irrigation ditches and earthen dams. Crayfish 

 also capture numerous small fish which are either immature food 

 fish or potential food of such fish, 



