GENERAL CHARACTERISTICS OF THE EASTERN SEAS 713 



column of the ocean. The works of Ya. Birstein, N. Vinogradova and Yu. Chin- 

 donova (1955, 1958) mark the beginning of this exploration. They have sub- 

 divided the pelagic area of the Pacific into zones. N. Vinogradova, moreover, 

 suggested a system of division for the bottom-living fauna (1955, 1956). 

 In later years all the Vityaz biologists were faced with this problem and it was 

 found that the same zonation scheme is applicable to the pelagic and bottom 

 life (Fig. 344) of the northwestern part of the Pacific Ocean.* 



This scheme is fairly similar to that of Y. Hedgpeth (1957). For the equa- 

 torial zone and for the Antarctic waters this scheme might require some 

 alterations. 



It is clear from this scheme that transitional horizons, where two neigh- 

 bouring faunas are intermingled, should be distinguished between the 

 sublittoral and bathyal as well as between the latter and the abyssal 

 (Table 289). 



Such zones as the supralittoral (above sea-level), the littoral (the tidal zone), 

 the sublittoral (the photosynthesis zone), the zone of the propagation of plant 

 organisms, the bathyal (the zone of the continental shelf), and the abyssal 

 (the zone of the ocean bed) are definite and established conceptions. The two 

 transitional horizons, a separate ultra-abyssal zone (zones of oceanic trenches) 

 and the division of the abyssal into two sub-zones need further explanation. 

 The convenience of this scheme has been checked on a series of groups of 

 invertebrates, the Pogonophorae, undoubtedly one of the most remarkable 

 groups of the bottom-living fauna of the Okhotsk and Bering Seas and of the 

 adjacent part of the Pacific Ocean. 



The first representative of this group (Siboglinum weberi) was described by 

 M. Caullerie (1914) from the collection of the Siboga expedition as a member 

 of a new family of a new group of animals. This first Pogonophora was found 

 in the waters of the Malayan Archipelago. The second specimen of the group 

 (LameilisabeUa zachsi) was found by Ushakov in the Bering Sea. A series of 

 new forms of this remarkable group of animals was found (A. Ivanov, 1949, 

 1952, 1955, 1957, 1959, 1960) at the beginning of the researches of the Vityaz, 

 when many new species of it were rapidly discovered. The place occupied by 

 Pogonophorae in the system of animal classification, as an independent group 

 of much taxonomic significance, was then determined (sub-phylum or even 

 phylum). Since the first research of Ivanov, the promoter of this remarkable 

 group, Pogonophorae were found in other places in the world ocean and in 

 the old collections of different expeditions, where they had been placed in jars 

 with polychaetes owing to the superficial resemblance of their tubes. Up to the 

 beginning of 1959 42 species of Pogonophorae have been recorded, but not 

 yet fully described, and assigned to 1 1 genera and a few families and orders. 

 The collections made by the Vityaz and other expeditions contain some dozens 

 of so far undescribed forms. New Pogonophorae forms are brought by every 



* At first the following terms were suggested for depths below 6 to 7 km and for the 

 fauna populating them: super-oceanic depths and super deep fauna (L. Zenkevitch, 

 1953). Later, however, Ya. Birstein suggested better terms — ultra-abyssal zone and ultra- 

 abyssal fauna. In 1956 the term Hadal (from the name of the mythological god Hades, 

 the ruler of the underground kingdom and the dead souls) was introduced by A. Brunn. 



