CHARACTERISTICS OF PELAGIC AND BOTTOM LIFE 327 



by Birstein (1959), as this report seems to me to be quite con- 

 vincing. 



As for the argument made by Menzies and Imbrie, it is first 

 noteworthy that the selection of material by these authors for 

 their analysis is entirely artificial and does not solve the problem, 

 i.e., "these groups were selected because for each there was 

 available bathymetric and paleontologic information that was 

 considered reliable enough to give useful results" (Menzies and 

 Imbrie, 1958). Since the authors state that "for the Echinodermata, 

 Arthropoda and MoUusca we have not been able to assemble 

 quantitative data on both age and depth distribution," it is clear, 

 as the authors themselves pointed out, that the most characteristic 

 groups of the present abyssal fauna do not come within the scope 

 of their analysis (i.e., Echinodermata, Arthropoda and Mollusca). 

 To this enumeration, we have added the Polychaeta, Pogonophora, 

 and Echiuroidea. I doubt that the authors include the most 

 typical representatives of the abyssal fauna related to these 

 groups, which either no longer inhabit the shallow-water zones, 

 never have lived there, or have originated in the ocean depths 

 themselves. If we disregard this last assumption, the endemic 

 species of the ocean depths should be considered as relics of earlier 

 geologic periods, even though they have not been found even as 

 fossils in shallow water. It is necessary to take into account the 

 fact that abyssal deposits are unknown to paleontologists. If 

 fossils of Pogonophora are not yet available, it should be ascribed 

 to the fact that the paleontologists do not yet recognize their tubes 

 or to their great age which dates back to the Proterozoic. In the 

 Paleozoic, they were already inhabitants of the ocean depths. 



To date about seventy species (not all of which have yet been 

 described) related to this group have been found in the ocean 

 depths. The Pogonophora doubtlessly are very primitive species. 

 The abyssal Polychaeta and Echiuroidea are likewise primitive. 

 Menzies and Imbrie suppose that Neopilina is the only repre- 

 sentative of the abyssal fauna discovered thus far as a fossil. But, 

 as you know, there are already two Neopilinas. Six species of the 

 genus Spinula (Malletiidae, Bivalvia) have been taken in the abyss 

 of the Pacific. Their known related forms are from Silurian 



