HABITS OF TROPICAL CRUSTACEA: III 



By R. P. COWLES 



Of the Department of Zoology, College of Liberal Arts, University of the 



Philippines, Manila 



ONE PLATE 



HABITS AND REACTIONS OF HERMIT CRABS ASSOCIATED WITH SEA 



ANEMONES 



The hermit crabs of the Philippine Islands form one of the 

 most interesting groups of the tropical Crustacea on account 

 of their peculiarities in structure and habits. Some of these 

 hermits have an asymmetrical abdomen, of such a shape that 

 the crab can insert it into the empty, spirally coiled shell of a 

 mollusk and carry the shell about as a protection against ene- 

 mies. Some hermit crabs of this kind spend practically all 

 their lives in the sea among the rocks and the corals -of rather 

 deep water; some live close to the shore in shallow water; and 

 others live far inland, visiting the sea only during the breeding 

 period, at which time they usually exchange their old shells 

 for new ones. Other hermit crabs have a straight, symme- 

 trical or almost symmetrical abdomen; one of these, Pylocheles 

 mdersii Alcock and Anderson, lives in the sea and inhabits a 

 joint of bamboo. Another kind, Birgus latro Linnaeus, the coco- 

 nut, or robber, crab, lives on land, carries no mollusk shell, and 

 like the ordinary land hermits visits the sea only occasionally 

 and possibly only at the breeding time. 



While the peculiar anatomy and fitness for the environment of 

 the hermit crabs are of interest, certain habits of these Crustacea 

 are even more interesting. The hermit begins life in the sea; 

 and, if it is of the ordinary kind that carries a spirally coiled 

 mollusk shell, it seeks and enters one of a size suitable to its body. 

 As the crab grows older it increases in size, thus necessitating 

 a change now and then to a larger shell. This habit is not a new 

 one to zoologists, for undoubtedly it has been observed many 

 times in many parts of the world. While, ordinarily, a hermit 

 occupies a shell of the right size for its body, it sometimes hap- 

 pens that the shell is too small, so that a large part of the anterior 

 portion of the body is exposed ; or that the shell is so large that 

 the crab can hardly be seen when it withdraws into the shell. 



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