. Essentials of biology presented in problems. Biology. 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 especia
. Essentials of biology presented in problems. Biology. 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 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 ane
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbiology, bookyear1911
