A-29 



variability seen throughout the survey. The fauna of the 

 depths between 800-1300 meters generally consists of two end- 

 member groups, shrimp (2) and the red crab Geryon quinquedens 

 and the witch flounder Gtyptocephalus oynoglossus (5) . 

 Figure D2 shows the depth distribution of Geryon quinquedens , 

 which was found in the depth range of 300-1600 meters within 

 our study area. In the south peak densities were encountered 

 at 1200-1250 meters where this crab extensively excavated the 

 semi-consolidated clay of the slope. Peak densities in the 

 north were found at 800-850 meters on the wall of Oceanogra- 

 pher Canyon. The depth range of G. quinquedens overlaps with 

 the lower range of the jonah crab Cancer borealis , but it was 

 never encountered in as high a density. 



Another faunal component of this middle zone is the quill 

 worm Hyalinoeoia artifex (3) , which when it occurred was 

 present in such high densities that it obscured the contribu- 

 tion of any of the other taxa within that sample. It has been 

 pointed out by Grassle et al., (1975) that the taxonomy of 

 Hyalinoeoia is quite complex, and thus, it is likely that more 

 than one species of this polychaete does exist within the 

 study area. The urchin Phormosoma placenta (10) is also 

 found within the middle depth zone. Like Hyalinoecia this 

 species tends to numerically dominate the fauna in areas where 

 it is seen. Both of these species tend to have a very patchy 

 distribution, characterized by high dominance in several of 

 the samples and almost complete absence in the other samples. 



