90 



Holothurians Ophiuroids 



Laetmophasma fecundum (?) Ophiura liilkeni (Lyman) 



Pannychia moseleyi (?) Amphiodia urtica (Lyman) 



Ophiacantha normani (Lyman) 2 



Numbers indicate number of station occurrences. Species without numbers were taken 

 only once. 



Discussion 



In order to provide explanations for the presence of distinct faunas in 

 these 12 environments just described and shown areally in fig. 27, one 

 must not only examine the physical characteristics of the environments, 

 but also the geological history of the region and the biology of the species. 

 The environmental boundaries are suggested both by the physical factors 

 and the distribution and abundance of the more important index animals. 

 One can readily see that a correlation is indicated between the distribution 

 of certain physical factors, such as temperature, depth, sediment type, 

 turbulence, oxygen and salinity, and the geographical limitations of most 

 invertebrates, since the distributional patterns of both the species and 

 physical factors coincide. On the other hand, the presence of some species 

 or even whole assemblages may not be determined by the physical factors 

 alone, but indirectly by biological factors, such as food preferences (which 

 in turn are mainly determined by feeding mechanisms), competition for 

 food, predator-prey relationships, reproductive capacity and larval 

 development, commensal or parasitic relationships, etc. 



One could gain an even better understanding of the organization of these 

 aggregations of animals if it were possible to determine numbers and 

 weights (biomass or standing crop) of the dominant and major sub- 

 dominant organisms within the assemblage. For instance, if the percentages 

 or biomass of animals involved in these various biological activities 

 (feeding and reproduction) were known within each community, some idea 

 of the energy relationships involved to sustain these communities could 

 be ascertained. This achievement has rarely been achieved for one assem- 

 blage, except by Sanders (1960), and no comparisons of this sort exist 

 for a number of assemblages in a single region, or between assemblages 

 from many regions. Unfortunately, standing crop and biomass figures 

 are not available for this study. 



Before discussing these various biological activities for each assem- 

 blage, it is first necessary to define the various terms used here. Feeding 

 types of invertebrates have been defined time and time again, so that 



