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, Pyloclieles 
miersii Alcock and Anderson, lives in the sea and inhabits a 
joint of bamboo. Another kind, Birgus latro Linmeus, 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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