16 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 22 



ophiuroid sample contains a large number of species, each with a few 

 representatives, except for the dominant members. In the latter case 

 samples from algal associations contain large numbers of species feeding 

 on rich grounds and the individuals of many species reach staggering 

 numbers. 



The offshore subsill areas of the basins support populations having 

 bio-indices of 3.0 or less, reflecting the lack of aggregation of individuals 

 of a species on areas of 0.25 square meter. Thus, members of a species 

 are widely separated statistically. 



The expression of bio-index, to have any meaning, must be limited in 

 its areal extent. Theoretical samples of large areal capacity, such as a 

 square kilometer, would have large bio-indices (calculated as 500,000 in 

 Santa Catalina Basin) and larger samples approach infinity, for specific 

 categories are limited in number while numbers of individuals are un- 

 limited. 



CHARACTERISTICS OF THE ANIMALS EXISTING IN 

 DEEP BASINS OFF SOUTHERN CALIFORNIA 



Most species are representatives of a few major groups (Appendix 

 VI). Polychaetous annelids with 109 species are the most abundant and 

 diversified. Echinoderms are represented by 13 kinds of ophiuroids, one 

 crinoid, three urchins and two holothurians. Sipunculids and nemerteans 

 are each represented by one or two species. Smaller crustaceans occur, 

 with 16 kinds of amphipods, six isopods, two cumaceans, an ostracod, a 

 ghost shrimp and a munnid crab. Mollusks are represented by about 8 

 living and 6 other dead kinds of pelecypods, four living and 2 dead kinds 

 of gastropods, three scaphopods, a chaetoderm, a chiton and dead ptero- 

 pod shells. Coelenterates, bryozoans, and an enteropneust are repre- 

 sented by one or a few specimens. Many species are tubicolous or burrow- 

 ing, existing in the sediments. They appear to occur in predictable ag- 

 gregates, so that the presence of one kind of species implies the presence 

 of other specific kinds. 



Most of the basin animals are small in size, ranging in length to a 

 few millimeters. They have a greater tolerance for reduced oxygen 

 supplies than do larger ones (Allee, Emerson, Park, Park & Schmidt, 

 1949, p. 343). A few are large and construct thick-walled mud tubes. 

 Ovigerous specimens often have relatively few, large and yolky eggs, 

 suggesting the presence of a short or no pelagic life. Individuals prob- 

 ably occur widely spaced since they number one to a few per sample. 



