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ZOOLOGY 



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 spiderlike legs, is neither an active runner or swimmer; it is, however, 

 protectively colored like the dark mud and stones over which it crawls. 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. 



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 

 living of animals in a mutually helpful relation is called symbiosis. 

 Of this we have already had some examples in plants as well as 

 among animals. (See Lichens, page 172.) 



Habitat. — Most crustaceans are adapted to live in the water; 

 a few forms, however, are found living on land. Such are the 

 wood lice, the pill bugs, which have the habit of rolling up into a 

 ball to escape attack of enemies, the beach fleas, and others. The 

 cocoanut crab of the tropics climbs trees in search of food, return- 

 ing to the water, at intervals, to moisten the gills. 



Giant spider crab from Japan. From photograph 

 loaned by the American Museum of Natural History. 



