718 



BIOLOGY OF THE SEAS OF THE U.S.S.R. 



Table 290 



Foraminifera, Hexacorallia, Nematoda, Polychaeta, Echiuroidae, Har- 

 pacticoida, Amphipoda, Isopoda, Gastropoda, Bivalvia and Holothurioidea 

 penetrate deepest of all. In contrast Bryozoa, Brachiopoda and Decapoda des- 

 cend least far into the depths. The deepest occurrence of fish — that of Care- 

 proctus amblystomopsis of the family Liparidae (A. P. Andriashev, 1955) 

 (Fig. 345) — was in the Kuril-Kamchatka trench at a depth of 7,230 m ; later, 

 however, this fish was recorded in the Japanese trench at a depth of 7,579 m. 

 This fish, according to Andriashev's terminology, is a secondary deep-water 

 dweller. The variety of species of the fauna decreases rapidly with increasing 

 depth, especially with the transition into the ultra-abyssal depths of the 

 trenches (Fig. 346). 



In the Kuril-Kamchatka trench 45 benthos species were found at a depth 

 of 6,860 m, 41 at 7,210 to 7,230 m, 20 at 8,330 to 8,430 m, 9 at 8,610 to 8,660 m, 

 18 at 9,000 to 9,050 m, and 6 at 9,700 to 9,950 m. 



The fact that the number of benthos species alone decreases with depth is of 

 special interest. Plankton behaves differently (Fig. 347). The highest qualita- 

 tive variety (calculated from Copepoda) is found not in the surface zone, but 

 at depths between 2,000 and 5,000 m. Unfortunately this phenomenon has not 

 yet been explained. It is best illustrated for Calanoidae in the Kuril-Kam- 

 chatka trench (Table 292). The same is noted in the case of pelagic Gammari- 

 dae {Table 293). 



Fig. 345. Careproctus (Pseudoliparis) amblystomopsis andriashev; absolute 

 length 238 mm. Kuril-Kamchatka trench, depth 7,230 m. 



