PARASITES AND MESSMATES 



211 



prey upon the Coral polypes, but all of which profit 

 by the fact that few enemies venture to pursue them 

 in their retreats. Innumerable prawn-like animals 

 of the Alpheidse and other families, and many kinds 

 of Crabs, are found among living Corals. The Crabs 

 of the family Trapeziidae are especially characteristic 

 of such habitats, and their thin, flat bodies seem to 

 be adapted to slip into slits and crannies of the Coral 

 blocks. The most highly specialized of all Coral 



Fig. 66 — Two Branches of a Coral {Seriatopora) showing 

 "Galls" inhabited by the Crab Hapalocarcinus marsupialis. 

 On the Right the Female Crab, extracted from the Gall 

 and further enlarged 



Crabs, however, are the species of the family Hapalo- 

 carcinidae, which modify in various ways the growth 

 of the corals on which they live. In some of the 

 more delicately branched kinds of Coral there may 

 sometimes be found hollow bulbous growths, each of 

 which contains imprisoned within it a little Crab — 

 Hapalocarcinus marsupialis (Fig. 66). It seems that 

 the female Crab (the habits of the male are not 

 definitely known) settles down among the branches 



