These environments and their assemblages are as follows: I. Intertidal 

 and shallow rocky shores; II. Intertidal beaches and sand flats to 10 meters; 

 III. Low salinity lagoons and mangrove mudflats; IV. Nearshore shelf, 

 sand bottom, 11-26 meters; V. Intermediate shelf, clayey-sand to sandy- 

 clay bottom, 27-65 meters; VI. Outer shelf, clay bottom, southern Gulf, 

 66-120 meters; VII. Outer shelf, sand bottom, northern Gulf, 66-120 

 meters; VIII. Northern Gulf basins and troughs, 230-1,500 meters; 

 IX. Upper slope, central and southern Gulf, 121-730 meters; X. Middle 

 slope, 731-1,799 meters; XI. Abyssal Southern Borderland basins and 

 lower slope, 1,800-4,122 meters; and XII. California Borderland basins, 

 1,641-2,358 meters (limit of sampling). 



The outstanding feature of the shallow water assemblages in the Gulf 

 of California is the great diversity of species in any one environment. A 

 survey of benthic communities throught the world, revealed no parallel 

 to this great diversity, whether in tropical or boreal regions. As many as 

 120 species of living mollusks were taken at numerous stations in the Gulf 

 in less than 60 meters. A check of unsorted dredge samples from off 

 Panama, revealed the same diversity there, indicating that great diversity 

 must be a characteristic of the Panamic province as a whole. No more 

 than a few individuals of any one species were taken by a grab or dredge 

 at any one station. Diversities were verified by cumulative curves based 

 on quantitative samples, compared with those made for European waters. 



A preliminary survey was made concerning the relationship of general 

 feeding types of invertebrates to the various environments. This survey 

 indicated that suspension feeders outnumber other feeding types on the 

 shallow sandy and intertidal rocky bottoms, while detritus feeders and 

 scavengers outnumber other types on clayey bottoms and at greater 

 depths. Although this is in accordance with other communities studied 

 elsewhere, the Gulf of California assemblages differed in the presence of a 

 tremendous number of predators, which remained rather constant from 

 shore to abyss. The relationship between feeding types and sediment type 

 did not hold true in the deeper portions of the shelf, where upwelling and 

 associated high surface productivity are a common phenomenon. Regard- 

 less of sediment type in these regions, suspension feeders still predominated. 

 Preliminary examinations of soft parts of some of these suspension feeders 

 indicate that they may capture the abundant organic detritus as it rains 

 down from the surface. There were also indications that there is a close 

 relationship between environment and larval development of mollusks. 

 Differing larval development of mollusks also offers an explanation for 

 some of the disjunct distributions of many forms along the coast of Middle 



