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environment (Goldberg and Parker, 1960). Not only is oxygen almost 

 non-existent in portions of the upper slope environment, but phosphate 

 concentrations are exceedingly high, reaching saturation point. This 

 correlation between high phosphate in the organisms and the environment 

 is therefore not too surprising. 



Two other invertebrates were abundant in the upper portions of the 

 "oxygen-minimum" zone off Baja California in the Pacific Ocean, a 

 gastropod, Nassarius miser, and a holothurian, Cucumaria chilensis. 

 Pleuroncodes occurred in such abundance at these localities that they 

 created the effect of a red sea at night. Trawling beneath these large surface 

 concentrations of Pleuroncodes produced an abundance of casts and parti- 

 ally decayed individuals (Boyd, 1963). It is possible that the decay of these 

 tremendous populations of Galatheids depletes the oxygen in this zone 

 and also provides the organic matter for the large numbers of Nassarius 

 and holothurians on the bottom. 



There are no comparable studies of the bathyal assemblage as a whole 

 in the literature, although bathyal invertebrates have been collected by 

 many expeditions and discussed in monographs for almost every phylum. 

 Dall (1886, 1889, 1890 and 1908) discussed at great lengths the mollusks 

 collected from both bathyal and abyssal depths along the Atlantic and 

 Pacific coast of the Americas. There are also many papers in existence on 

 other invertebrate groups from bathyal depths, resulting from the various 

 cruises of the American fisheries vessel, Albatross. It is too difficult, at 

 the moment, to attempt a compilation of all the species by station, in 

 order to determine the assemblages or communities found. This same draw- 

 back applies to the "Challenger", "Siboga" and other major deep sea 

 expeditions. Even Ekman's (1953) discussion of the bathyal fauna gives 

 little indication of the association of animals to be found. He also con- 

 fined his treatment to north Atlantic depths, where the fauna has little 

 resemblance to that found in tropical bathyal regions. Sparck (1951) took 

 several quantitative grab samples at lower bathyal to abyssal depths off 

 West Africa but did not list the species. 



Even though the majority of the species of animals in this environment 

 are deposit feeders or scavengers (on the basis of anatomy), 26% of the 

 species can be classified as suspension feeders, a rather high percentage 

 for these depths. This relatively high percentage of suspension feeders 

 probably subsist on the rain of organic matter resulting from the high 

 primary production in the surface waters of this zone. The high primary 

 production on the surface seems to be one of the major causes of the 

 "oxygen-minimum" zone, since blooms are often found overlying strong 



