THE JOINTED-FOOT ANIMALS 



161 



The chelipeds are abnormally developed and, besides being 

 of use in capturing prey, serve the important function of 

 closing the aperture of the shell in times of danger. 



Hermit crabs live in great abundance along gravelly 

 beaches, where they are useful scavengers of dead animals 

 in the water. In spite of the heavy houses which they carry, 

 they move about with surprising facility. As suggested by 

 one observer, they are wary, cunning, belligerent, and 



Fig. 87. Blue crab and hermit crab, (x J) 



cowardly, making great pretense of fighting, but on the first 

 show of force by an opponent withdrawing into their shells. 

 A small, shore species more frequently seen never becomes 

 as large as Pagurus pollicaris, which is a deep-water species. 

 All the species, however, when the individuals are young, 

 choose small shells ; as they grow older and larger after each 

 molt, the unused space in the shell becomes less and less. 

 Naturalists have observed the action of hermit crabs that 

 have become too large for the shell. The animal searches 

 about for a suitable larger shell, and when it finds one 

 withdraws its body from the old shell and extends it into 

 the new. 



