DECAPODA 



393 



Fig. 626 , 

 Hippa talpoida 

 (Verrili). 



FAMILY 1. HIPPIDAE. 



Cephalothorax cylindrical, with the abdomen bent under it; telson 

 triangular and elongate; first pair of periopods not chelate: 3 genera and 

 about 20 species, which burrow in the sand. 



HIPPA Fabricius. Second antennae long and fringed, with long hairs 

 on its hinder surface; eye stalk very long: 2 species, 1 American. 



H. talpoida Say. The sand bug (Fig. 626). 

 Length 25 mm.; color whitish tinged with purple on 

 the back: Cape Cod to Florida; Pacific coast; very 

 common on sand bottoms and beaches, in which it 

 burrows with great rapidity. 



FAMILY 2. PAGUEIDAE. 



Hermit crabs. Cephalothorax flattened, and with 

 a hard shell; abdomen usually asymmetrical, elon- 

 gate, and soft ; eye stalks long ; first pair of periopods 

 large and chelate, last pair reduced in size and extend- 

 ing backwards and upwards, abdominal appendages rudimentary or 

 wanting, the last pair used to hold the animal in the snail shell in which 

 it lives. Allied to the hermit crabs is one of the most remarkable terrestrial 

 decopod crustaceans, Birgus latro, the palm crab of the Pacific. It lives in 

 holes in the ground and seldom goes into the water, but breathes air, the gill 

 chambers being converted by the presence of a network of blood capil- 

 laries into lungs, while the gills are 

 very small. Its food consists of cocoa- 

 nuts, which, however, it does not climb 

 the trees to get, as it is popularly 

 supposed to do. The family contains 

 about 20 genera. 



PAGTJKUS Fabricius. First pair of 

 antennae short, second pair long; right 

 claw usually the larger : the animal 

 lives in the empty shell of some marine 

 snail which it carries about with it, and 

 as it increases in size changes for a 

 larger one; the shell is frequently more or less covered with colonies of 

 a hydroid, Hydractinia echinata, with which it lives in commensalism, 

 the hydroid enlarging the shell by building up its free edge and thus 

 saving the crab the necessity of changing its abode; over 100 species. 

 P. longicarpus Say. Small hermit crab. Chelae smooth and elon- 

 gate: very common from Maine to South Carolina, usually inhabiting the 

 shells of small snails in rock pools and shallow water along the beach. 



Fig. 627 Pagurus pollicaris, out of 

 its shell (Paulraeier). 



