176 ANIMAL LIFE 



This sea-anemone is fastened securely to the shell, and has 

 its mouth opening and tentacles near the head of the crab. 

 The sea-anemone is carried from place to place by the her- 

 mit-crab, and in this way is much aided in obtaining food. 

 On the other hand, the crab is protected from its enemies 

 by the well-armed and dangerous tentacles of the sea-anem- 



FIG. 105. Hermit-crab (Pagurus) in shell, with a sea-anemone (Adamsia pattiata) 

 attached to the shell. After HERTWIG. 



one. In the tentacles there are many thousand long, 

 slender stinging threads, and the fish that would obtain 

 the hermit-crab for food must first deal with the stinging 

 anemone. There is no doubt here of the mutual advan- 

 tage gained by these two widely different but intimately 

 associated companions. If the sea-anemone be torn away 

 from the shell inhabited by one of these crabs, the crab 

 will wander about, carefully seeking for another anemone. 

 When he finds it he struggles to loosen it from its rock 

 or from whatever it may be growing on, and does not rest 

 until he has torn it loose and placed it on his shell. 



There are numerous small crabs called pea-crabs (Pin- 

 notheres) which live habitually inside the shells of living 



