138 



PRACTICAL ZOOLOGY 



structural modifications. The lobsters, shrimps, prawns, spider 

 crabs, hermit crabs, edible crabs, and fiddler crabs are all dec- 

 apods. The rest of the Crustacea are for the most part small 

 and inconspicuous. The barnacles have a very remarkable 

 life history. Some of the other species, like the sow bugs, have 

 become terrestrial in habit. Most Crustacea live in the sea; a 

 great many species, however, live in fresh water, including the 

 one-eyed Cyclops, the water flea, Daphnia, and the fairy shrimp. 

 Branchipus. 



FIG. 78. Photograph of hermit crab in snail shell. (From Caiman.) 



Crabs. - - The crabs differ from the crayfish in having a very 

 small abdomen which is folded under the large, broad cephalo- 

 thorax as in the blue or edible crab (Fig. 77, A). The spider 

 crabs are curious-looking creatures with long, stiltlike legs which 

 carry them over the rough sea bottom with ease. One species 

 living in Japan is said to measure twenty feet from tip to tip of 

 the first pair of legs. The fiddler crabs (Fig. 77, B) are curious 



