DISTRIBUTION OF PACIFIC DEEP-SEA ANIMALS 367 



Antarctic) ; it was found in the Indian Ocean (£. paradoxa Mortensen) 

 and in the South West Pacific (£. phiale [Wyv. Thomson]). 



Finally may be mentioned a fish Bathymicrops regius Koefoed, 

 known since the Michael Sars Expedition in 1910 from the North At- 

 lantic, caught there again by The Swedish Deep-Sea Expedition (Ny- 

 belin 1951), and found in the Indian and Pacific Oceans by the Gala- 

 thea (Fig. 1). 



More examples of this kind could be given, and many more will 

 surely be added when present and future collections have been studied. 

 At the same time the confused state of taxonomy of many deep-sea ani- 

 mals may be cleared up, and present apparent differences in the com- 

 position of the faunas may also be reduced in this way. 



All this would lead to the postulate that the Pacific abyssal and 

 abysso-pelagic fauna is part of the Cosmo^^olitan true deep-sea fauna. 

 This is really to get back to the views held in the early days of deep-sea 

 research. But this does not mean that differences in the composition 

 of the animal communities from one area to another would not be 

 found; indeed, they will occur and arise from two major ecological fac- 

 tors: 1. Depth (= pressure) and 2. Supply of food. 



The importance of pressure has been evidenced very clearly from 

 ZoBell's studies (1953) of the barophilic bacteria, especially from the 

 Galathea samples from the deep trenches, right down to 10000 meters. 

 The distribution of many abyssal animals indicates that they may also 

 be called barophilic, e.g., Bathymicrops (Fig. 1) or sthenobathic; another 

 group, like Pourtahsia and Elpidia mentioned above, seem to be eury- 

 bathic, as no morphological differences have been found within the 

 enormous vertical range. The presence of physiological differences, 

 however, cannot be excluded and seems quite likely. 



Zenkevitch (1953) relates that Russian investigations in the Kurile- 

 Kamtschatka Trench, tra^vling down to 9800 meters gave the following 

 zonation: 



I Surface zone, influenced by winter cooling, 0-200 m. 



II Transition zone, warm oceanic water masses, 200-500 m. 



III Deep-sea zone, 500-6000 m. ("normal ocean depths") 



1. Upper subzone, 500-2000 m. 



2. Lower subzone, 2000-6000 m. 



IV Deep-sea trenches ("super oceanic depths") 6000-10000 m. 



In accordance with the general impression derived from earlier 

 investigations (for literature see Ekman 1953a) and the collections of 

 the Galathea, keeping the abyssal zone from 2000 meters and down- 

 wards seems more natural. Vertically this zone may then tentatively 

 be divided in three: 1. Depth range 2000-4000 meters, 2. Depth range 



