testing and feeding in a large volume of water by cephalopods and crus- 

 taceans, and the weak development of the eyes of deep-water decapods and 

 mysids. For example, Chiroteuthis and M astigoteuthis have greatly 

 elongated tentacles, which may be 5 or 10 times as long as the body. The 

 anterior appendages of certain predaceous deep-water Copepoda are greatly 

 enlarged by lengthening of the segments of the basipodite of the second 

 maxiliipeds and have sparse but long, strong setae. In a living specimen 

 (Wickstead, 1962), the feeding appendages are extended downward and 

 forward and form a trap which snaps shut whenever prey enters it. However, 

 the predaceous copepods do not attempt to follow prey which floats past. 



Thus, the adaptations related to the peculiarities of existence 

 and attempts to reduce the expenditure of energy are quite radical and 

 varied. They change the appearance of pelagic deep-water animals much 

 more than do adaptations to changes in other factors of the environment. 

 In other words, changes in the food supply, not changes in physical 

 parameters such as light, pressure or temperature, are most important in 

 determining the peculiarities of morphology of the pelagic animals at 

 different depths. 



The principle of economy of energy expenditure is apparently not 

 limited to a decrease in the level of basic and active metabolism. In 

 the opinion of V. Walters (1961), one important path of evolution in 

 waters poor in food resources, such as at great depths, is neoteny. 

 Neotenic development eliminates the catabolic phases of the life cycle 

 and the morphogenesis of "mature" structures. As a result, the animals 

 need less energy for the attainment of sexual maturity. 



Peculiarities of the breeding of deep-water animals are also related 

 to the acquisition of food. Two paths of development of juveniles are 

 possible for inhabitants of the food-poor deep waters: either production 

 of a large number of small eggs, with the small, weak larvae feeding in 

 the food-rich surface zone, or the production of a small number of large 

 eqgs, rich in vitellus, so that the embryos can pass through a number of 

 metamorphic stages before hatching. The large, lecithotrophic larvae, 

 when they first hatch, need not (or almost need not) feed, if there is 

 no suitable food available, and later are capable of utilizing large, 

 scattered food objects, which could not be eaten by planktotrophic larvae. 

 The former path is characteristic for most deep-water pelagic fish. The 

 latter has been followed by only a few, primarily benthic, deep-water 

 species (certain Apoda, some of the Macruridae, Liparidae, etc.), although 

 this path is followed by the overwhelming majority of deep-water higher 

 crustaceans (Decapoda, Amphipoda, Euphausiacea, Mysidacea, etc.) and 

 many Cephalopoda. 



The direction of evolution is also related to a great extent to the 

 food resources: Where food is abundant, highly fertile species are 

 primarily produced, with short life cycles and a broad range of adaptation, 

 while under conditions of limited food supply, relatively less fertile, 

 narrowly specialized species with long life cycles are found (Shmal 'gauzen, 

 1968). The abundance of food resources also defines the structure of the 

 pelagic communities at various depths. 



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