NO. 2 OLGA hartman: submarine canyons 19 



hydroids, ophiuroids, nestling mollusks and a few other species com- 

 prised the population ; this is a rock bottom fauna. 



Another sample trawled Oct. 31, 1958, at the head of Santa Monica 

 canyon, 7 miles from shore, centered at 33° 54' 00", 118° 36' 00" 

 in about 200 meters, yielded large boulders of which the exposed sur- 

 faces were sparsely covered with animals, including branching hydroids 

 and small colonies of encrusting bryozoans. A large cherty boulder 

 was riddled by holes of a boring clam, Saxicava arctica. Small chitons 

 and nestling maldanids occupied the depressions and silt-covered pockets 

 of the rock. 



Polychaetes include Aricidea sp. ; Dodecaceria sp., small but oviger- 

 ous individuals; Eulalia sp., dorsum yellow, with 3 black spots to each 

 segment; Eunice multipectinata; Exogone sp., with long swimming 

 setae; Drilonereis sp., drab green with pale prostomium ; Glycera 

 tenuis; humbrineris index ; Notoproctus pacificuSj in arenaceous, fragile 

 tube ; Nicomache personata, large red, in arenaceous tubes in rocky 

 depressions; Oncoscolex pacificus; Pherusa papillata; Peisidice aspern; 

 Lepidonotus caelorus ; Lagisca multisetosa; harmothoid polynoids ; 

 Sphaerodorurn papillifcr; protulid tube, cylindrical, smooth, fully at- 

 tached to rock. 



Echinoderms include Allocentrotus fragilis; Ophiopholis bakeri; 

 Ophiura liitkeni; Ophionereis eurybrachyplax; Ophiodesmus amphilogus. 



Mollusks include small chitons; small gastropods; Saxicava arctica. 



In addition, there were also a sipunculid, articulate brachiopods, 

 solitary corals, amphipods, a gnathid isopod, encrusting bryozoans. 

 This is a rocky fauna. 



In Santa Monica canyon, the shallowest grab samples, in 116 and 

 183 meters, came from, axes depths and yielded animals limited to 

 Capitella capitata subspp. and Dorvillea articulata, both indicating a 

 disturbed or lowered salinity condition. At 268 meters an abrupt 

 faunal change is indicated by the large numbers of shelf species. At 

 330 to 479 meters the presence of high numbers of Maldane sarsi 

 indicates a change from sandy to silt bottom. An Onuphis vexillaria 

 association is best represented in depths of 454 to 583 meters; this is 

 replaced in 542 meters and beyond by deepwater species, not occurring 

 in shallower bottoms. The deepest parts of the canyon, from 800 meters 

 down, is nearly or altogether dead, like the basin. 



