THE CRUSTACEANS 



93 



Fig. Oo: IIKHMIT CRAH. Knui] \Aie. Sliowing 



the liorr'tnved shell rovered Willi sea weeds 



ahd HydracHnia. Cape Ann, Mass. 



the crab instantly witlidraws witliin its shell, completely closing 



the opening with its claws, whicli arc of the exact shape 



retpiired for the purpose. 



As the crab grows it . 



must occupy larger and 



larger shells. These are 



apparently selected with coii- 



sideraljle care, but liiuiiig 



decided upon it tlie crab 



finally darts into its new 



abode with almost incredible 



rapidity. in common witli 



other crustaceans tliese craljs 



are scavengers. • They are 



also inveterate fighters, and 



will conquer and devour one 



another when opportunity 



offers. A niunljer of marine 



animals grow upon the sliells, 



which are carried^aliout by hermit crabs, thus obtaining the advan- 

 tages of a Avandering life. Several species of hydroids. such as 



Uydractinia, cover the shells 

 with soft, pink-white, velvety- 

 looking growths, while anum- 

 Ijer of sea anemones also live 

 u])on the shells. One of these 

 called ( Epizoanllms iivierica- 

 7iiisJ finally dissolves the shell, 

 forming a cavity within which 

 the cral) continues to reside. 

 One of the most interest- 

 ing of the hermit crabs is the 

 Robber Crab ( Birgun lolroj of 

 the tropical Pacific Islands. It 

 is about two and a half feet 

 long, and the abdomen is soft 

 below but protected above by 



hard plates. It lives within deep burrows, and only occasionally 



visits the water. It crawls to tlie top of the cocoanut trees, and 



tears open the nuts for the sake of the white "meat." 



Fig. 1,1 : HEU.MIT CRAH. 

 Gape Ann, Mass, 



