131 



abyssal fauna on a single catch basis can be found in Murray (1895), 

 Weber (1902), Nybelin (1951), Zenkevitch, etal. (1955), Bruun (1957), 

 SuYEHiRO, etal. (1960) and Wolff (1960). 



As is to be expected, the majority of the species of animals living in the 

 abyssal borderland and slope environment are deposit feeders, most of 

 which are moUusks and echinoderms. Nothing is known concerning 

 reproduction of these species. Further research on deep sea animals should 

 now be concentrated on the biology of these animals, rather than zoo- 

 geography, but this will necesitate far more sophisticated sampling 

 techniques than are now available. 



A check was made as to the abyssal character of the molluscan species 

 taken in this environment, by using Clarke's (1962) compilation of 

 abyssal mollusk records from the literature. Altogether, 27 species of 

 mollusks were identified from the lower slope and southern borderland. 

 Of these, 18 were listed as abyssal by Clarke. Those species not considered 

 new have also been taken in slightly shallower depths, but farther north, 

 and would still be considered abyssal on the basis of temperature. The 

 majority of the other invertebrates have been collected only in abyssal 

 depths, indicating the true abyssal character of this assemblage. 



Surprisingly enough, elements of this same abyssal assemblage have 

 been reported from Pliocene sediments in Costa Rica, Panama and Ecuador 

 (Olsson, 1942). Typical abyssal and bathyal genera, sub-genera and 

 species of mollusks, directly related to forms taken in depths of between 

 500 and 3,000 meters on the adjacent slope were well-preserved in dark 

 shales and sandstones, which must have been uplifted several thousand 

 feet. 



XII. California Borderland Basins, 1,641 to 2,358 Meters: 



As mentioned previously, the differences in the fauna of the northern 

 basins along the California coast seem to be sufficient to constitute a 

 different assemblage, partly abyssal in nature. Of the mollusks found in 

 this environment, Clarke (1962) reports only 8 of the 25 species as being 

 abyssal. The rest have been reported as either bathyal or as Arctic shelf 

 species. It was also observed that most of the fish taken from the Cali- 

 fornia borderland region were either shallower water species or had pre- 

 viously been taken on the continental shelf of the northern and north- 

 western Pacific (HuBBS, personal communication). 



It is puzzling as to why the California borderland basin assemblage is 

 so different from that found at equivalent depths to the south, since 

 temperature, oxygen and sediment conditions are similar in both areas. 

 The only feasible explanation for this separation of faunas is that the 



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