NO. 2 OLGA HARTMAN: SUBMARINE CANYONS 41 



In 755 meters, with 1.8 grams:. 



a nemertean 55.5% 



polychaetes 27.8 



solenogasters 16.7 



In Mugu canyon, therefore, brissopsids and echiuroids were highest 

 in biomasses, followed by polychaetes, mollusks and nemerteans. 



Dume canyon: — Weights of animals dropped almost directly with 

 depth from a high of 307.4 grams to a square meter, to zero at its 

 lowest depth. These values are as follows : 



307.4 gm/ sq.m., in 299 m. 1 12.78 gm/ sq.m., in 638 m. 



214.56 gm/ sq.m., in 374 m. 36.7 gm/ sq.m., in 71 1 m. 



202.4 gm/ sq.m., in 398 m. 32.4 gm/ sq.m., in 652 m. 



188.4 gm/ sq. m., in 181.6 m. 6.0 gm/ sq.m., in 741 m. 



181.6 gm/ sq.m., in 530 m. no life in 905 meters. 



The sediments in these samples were silt or mud, except in 374 m, 

 where they were sand. Biomasses by animal groups gave the following 

 results : 



In 299 meters, with 153.7 grams: 



3 brissopsid urchins 74.5% 

 polychaetes 25.5 



In 374 meters, with 536.4 grams: 



2 echinoids 50.56% 



polychaetes 46.28 

 siliceous sponge 2.79 



all others, less than 1.0 



In 398 meters, with 50.6 grams: 



polychaetes 96.05% 



mollusks 3.96 



In 507 meters with 47.1 grams: 



4 echinoids 84.9% 

 polychaetes 13.7 



a ghost shrimp 1.7 



In 530 meters, with 90.8 grams: 



5 brissopsids 69.38% 

 polychaetes 16.63 

 shelled mollusks 13.99 



