CHARACTERISTICS OF PELAGIC AND BOTTOM LIFE 



325 



1. Phascolion Intense (Sipunculoidea). 3606-7340 m 



2. Tatjanellia grandis (Echiuroidea), 2970-3400 m 



3. Scina wagleri var. abyssalis (Amphipoda), >6000 m 



4. Miinidopsis antonii (Decapoda), 2520-3900 m 



5. Glyphocrangon rimapes (Decapoda), 2510-3120 m 



6. Nymphon procenim (Pantopoda), 2430-4600 m 



7. Hymenaster anomalus (Asteroidea), 2059-2608 m 



8. Kolga nana (Holothurioidea), 2245-4750 m 



9. Cideolus shiimi (Ascidia), 2894-4716 m 

 10. Cideolus murrai (Ascidia) 3397-4630 m 



Fig. 1. Some examples of bipolar distribution of the abyssal fauna. 



sediments or of the bottom water layer just above the bottom may 

 determine their distribution. This is a mere hypothesis. Perhaps 

 also, the tectonic processes due to volcanic activity, the out- 

 cropping along lines of fracture, the accumulation of radioactive 

 substances and rare elements in a particular area, a certain gas in 

 the near-bottom layer may all contribute to defining local bio- 

 geographical pro\inces. These might provide effective barriers for 

 abyssal organisms which are especially sensitive to one or another 

 of these factors. I illustrate this point with a photograph from the 

 eastern Pacific taken by my son, N. Zenkevitch, at a depth of 

 4000 m (Fig. 2). What else can be compared with these "cobble- 



