7 6 



SYSTEMATIC ZOOLOGY 



animals, and one of these is strikingly like that mentioned in 

 connection with the hydroid polyps. Here a species of sea 

 anemone becomes attached to the shell in which a hermit 

 crab lives (Fig. 61), and thus gets the benefit of being carried 

 about from place to place, and at the same time serves to conceal 

 the crab from its enemies. The corals, which, as we have said, 



I 



etc 



FlG. 61. Adam.iia palliata, four individuals attached to a gastropod shell inhabited by a 

 hermit crab, nc, ac' , acontia; sh, portion of gastropod shell. (After Andres, from Parker 

 and Haswell's Text-book.) 



are almost exclusively tropical, never grow in water over eighty 

 meters deep, and many species grow in much shallower water. 

 The red coral lives in the Mediterranean only, and is found 

 in water from twenty to sixtv meters deep. The skeletons 

 of corals play a very important part in the formation of main- 

 tropical islands and of reefs which break the force of the 



