114 



centage of suspension feeders, which could take advantage of these plank- 

 ton blooms. Analyses of feeding types of the dominant members of benthic 

 communities has seldom been attempted, although Sanders has done so 

 in both Long Island Sound (Sanders, 1956) and in Buzzards Bay, Massa- 

 chusetts (Sanders, 1958, 1960), and apparently by Savilov (1961) and 

 TuRPAEVA (1957), which were not available in their entirety to this author. 

 For instance, in Buzzards Bay, Sanders (1960) indicates that in the silty- 

 clay, Nephthys incisa-Nucula proxima community, the most abundant 

 three species are selective and non-selective deposit feeders, the fourth 

 ranked species is probably a carnivore, and the fifth a suspension feeder. 

 Of the 30 most abundant (by number, but not necessarily by weight) 

 species of invertebrates in this community, 10 or SS^/o are selective deposit 

 feeders, 8 or 26% are non-selective deposit feeders, 4 or 14% are suspension 

 feeders, 6 or 20% are carnivores, and the remaining V'/,, are scavengers and 

 one specialized deposit feeder {Turbunilla). Earlier, Sanders (1958) re- 

 marked that in Buzzards Bay, 80 to 99% by number of benthic fauna 

 comprised the primary consumers, i.e. herbivores and detritus feeders. 

 The filter or suspension feeders made up the majority of the fauna of sandy 

 sediments, while deposit feeders dominated the fauna on clay bottom. In 

 the sand-bottom Ampelisca community, suspension feeders constituted 

 two-thirds of the population by number, while 80% of the fauna of the 

 silty clay, Nephthys- Niiciila community are deposit feeders. This same 

 relationship between fine sediments and feeding types was also found by 

 Sanders to exist in Long Island Sound (Sanders, 1956, 1958). Sanders 

 results are therefore in relatively close agreement with those found in the 

 present study for the shallow waters of the Gulf of California. McNulty, 

 Work and Moore (1962), in a study of level bottom communities of south 

 Florida in somewhat comparable depths, but carbonate rather than 

 terrigenous sediments, offered several generalizations regarding the 

 relationship between feeding type and sediment size. Since terminology 

 differs from that used here, direct comparisons are difficult. They found 

 that detritus feeders predominate in the finest sediments, and deposit 

 and filter feeders at intermediate size grades. However, their sediment data 

 indicates that on the whole, grain size is much larger in Biscayne Bay, 

 Florida than in the nearshore environments of the Gulf of Mexico. 



Two thirds of the index or characteristic 21 species for this environment 

 most likely have planktonic larval development, while the other third 

 could have non-planktonic development. Since nothing was known con- 

 cerning the exact reproduction of many of the Gulf of California species 

 of mollusks under discussion, larval development types were often hypo- 



