. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. 224 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
. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. 224 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 Giant spider crab from Japan. From photograph loan
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