230 



THE CRAYFISH 



ditions by curling around in the spiral snail shell, so that it has become 

 asymmetrical. These tiny crabs are great fighters and wage frequent 

 duels with each other for possession of the more desirable shells. They 

 exchange then- borrowed shells for larger ones as growth forces them from 

 their first homes. 



The habits of these animals, and those of the fiddler crabs, might be 

 studied with profit by some careful boy or girl who spends a summer 

 at the seashore and has the time and inchnation to devote to the work. 

 Of especial interest would be a study of the food and feeding habits of 

 the fiddler crabs. 



A deep-water crab often seen along Long Island Sound is the spider 

 crab, or "sea spider," as it is incorrectly called by fishermen. This 



animal, with its long spider- 

 like legs, is neither an active 

 runner nor swimmer ; it is, 

 however, colored like the dark 

 mud and stones over which it 

 crawls ; thus it is enabled to 

 approach its prey without be- 

 ing noticed. The resemblance 

 to the bottom is further 

 heightened by the rough body 

 covering, which gives a hold 

 for seaweeds and sometimes 

 sessile animals, as barnacles, 

 hydroids, or sea anemones, 

 to fasten themselves. 



A spider crab from the Sea 

 of Japan is said to be the 

 largest crustacean in the 

 world, specimens measuring 

 eighteen feet from tip to tip 

 of the first pair of legs having 

 been found. 



Giant spider crab from Japan. From photograph 

 loaned by the American Museum of Natural 

 History. 



Symbiosis. — Certain of the spider crabs, as well as some of the 

 larger deep-water hermit crabs, have come to live in a relation of 

 mutual helpfulness with hydroids, sponges, and sea anemones. 

 These animals attach themselves to the shell of the crab and are 

 carried around by it, thus receiving a constant change of position 

 and a supply of food. What they do for the crab in return is not 

 so evident, although one large Chinese hermit regularly plants a 

 sea anemone on its big claw ; when forced to retreat into its shell, 

 the entrance is thus effectually blocked by the anemone. The 



