394 



CRUSTACEA 



P. pollicaris Say (Fig. 627). Large or warty hermit crab. Chelae 

 covered with tubercles, and very wide and stout, and used by the animal 

 to close the opening of the shell: Maine to Florida, usually inhabiting 

 the shells of Fulgur, Natica, or other large snails in deeper water along 

 the shores. 



Suborder 2. BRACHYURA. 



Crabs. Cephalothorax short and broad, with the small abdomen 

 bent under it; abdomen of the male very narrow, with rudimentary legs 

 and fitting into a groove of the ventral surface of the cephalothorax; 

 abdomen of the female broad, with 4 pairs of well-developed biramose 

 legs to which the eggs are attached; antennae very short and often foot- 

 like; third pair of maxillipeds flat and plate-like and covering the other 

 mouth parts ; the 5 pairs of periopods well developed, the first pair form- 

 ing the large pinching claws; the abdominal legs much reduced, from 1 to 



4 pairs being present; no 

 uropods present; young usu- 

 ally born in the zooea stage 

 and pass through the mega- 

 lopa stage before reaching 

 maturity (Fig. 628). 



The crabs are the high- 

 est crustaceans. They occur 

 mostly in the sea, living on 

 or near the bottom, from tide 

 lines to very great depths. 

 Some, however, like the blue 

 crab, swim very well and rapidly and are frequently seen near the 

 surface. Some species, like the fiddler crabs and the sand crabs, live 

 near the high-water line or above it and have become to a greater or 

 less degree terrestrial animals. They run about rapidly over the sand, 

 in which they dig deep burrows, and their gills and gill chamber are 

 especially adapted to the absorption and retention of moisture from 

 the damp sand. Still other crabs, as those belonging to the Gecarci- 

 nidae, the land crabs which are often distinguished by their large 

 size, are found habitually far from the water, to Avhich they return period- 

 ically to deposit their eggs. Cardisoma guanliumi, the common land crab 

 of the West Indies and Bermuda, occasionally makes its appearance in 

 Texas. The crabs of the family Thelpliusidae live exclusively in fresh 

 water, the best-known representative being Thelpliusa fluviatilis, the com- 

 mon fresh-water crab of southern Europe. The suborder contains 4 

 divisions. 



Fig. 628- 



-Larvae of crab (Claus), 

 B, megalopa. 



A, zooea : 



