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ANIMALS AND THEIR ENVIRONMENT 



Figure 38.11. Sexual parasitism in the deep-sea angler fish, Photocorynus spi- 

 niceps, in which the difficulty of one sex finding the other is met by permanent 

 attachment of the much smaller male to the female. The union is so complete that 

 the male has no independent existence at all, being nourished by the blood of the 

 female to which he is attached. (After Norman, from Allee et al.: Principles of 

 Animal Ecology.) 



elude the Portuguese man-of-war, jellyfish, squid, fishes and whales. 

 Some whales are equipped with strainers and feed upon the microscopic 

 plankton; others have teeth and prey upon fish, squid and other whales. 



The abyssal region, lying below the pelagic, is characterized by the 

 absence of light and the consequent absence of living green plants. The 

 waters are quiet and very cold and the pressure is stupendous. The ani- 

 mals that live here feed upon each other and upon the bodies of dead 

 plants and animals that are constantly settling down from above. Most 

 of the fish of the abyssal region are small and peculiarly shaped; many 

 are equipped with luminescent organs, which may serve as lures for their 

 prey. The majority of the deep-sea creatures are related to shallow-sea 

 forms and are believed to have migrated to their present habitat rela- 

 tively recently (by geologic standards), for none is older than the 

 Mesozoic. 



Since the number of members of any one species in these vast, dark 

 depths is small, reproduction is more of a problem than in any other 

 region, and some fish have evolved a curious adaptation to ensure that 

 the two sexes will be in proximity to reproduce. At an early age the 

 male becomes attached to the head of the female and fuses with it. There 

 he continues to live as a small (inch-long) parasite (Fig. 38.11). In due 

 course he becomes sexually mature and when the female lays her eggs, 

 he releases his sperm into the water to fertilize them. 



The bottom of the sea is a soft ooze, composed of the organic re- 

 mains and shells of foraminifera, radiolaria, and other animals and 

 plants. Many invertebrates live at great depths on the ocean floor, and 

 characteristically have thin, almost transparent shells, whereas the related 



