ZOOPLANKTON OF CENTRAL PACIFIC 



367 



Fir; 1 RE 2. — Plankton-station positions of Hugh M. Smilh cruises 15 (May-June 1952), 16 (August 1952), and 18 (October- 



Xovember 1952). 



duration to a deptli of about 200 meters were eni- 

 ploycd on most cruises. On the Hugh At. Smith 

 cruise 14, multiple-net horizontal hauls were made 

 at 7 stations. Methods of hauling and calcula- 

 tion of sampling depth and amount of water 

 strained have been explained in previous reports 

 (King and Demond, 1953; King and Hida, 1954). 



TREATMENT OF SAMPLES IN THE LABORATORY 



First the few organisms with longest dimension 

 greater than 2 cm. were removed from each sam- 

 ple, identified as precisely as possible, and their 

 displacement volume determined. Then the vol- 

 imie of the remainder and bulk of the sample, i. e., 

 those organisms with longest dimension less than 

 2 cm., was determined. In measuring the dis- 

 placement volume, the plankton was poured in a 

 draining sock of 56XXX grit gauze, to filter ofi" 

 the preserving liquid. When the sample stopped 

 dripping, it was transferred to a graduated cylin- 



der of appropriate size (usually 50 or 100 ml. ca- 

 pacity). By means of a burette, a known volume 

 of water was added to the drained plankton. The 

 difference between the volume of the plankton 

 plus the added liquid and the volume of liquid 

 alone was recorded as the displacement or wet 

 volume of that portion of the sample. 



Following the procedure at our laboratory, the 

 volume of all organisms less than 2 cm. in length 

 plus the volume of organisms 2 to 5 cm. in length 

 that might be considered of significant nutritional 

 value ^ were combined to give a single volume 



' We consider annelids, chaetognaths, crustaceans, c^ptialopods, and flsb 

 to he of significant nutritional value, and siphonophores, medusae, cteno- 

 I)hores, heteropods, and tunicates as non-nutritious. Bigelow and Sears 

 (ia39) and also Clarke (194(1) considered the crustaceans, chaetognaths. and 

 nioUusks as being of high nutritive value. It Is our judgment, that the 

 heteropod mollusks of the family I'terotracheldae, which are of common 

 occurrence in the plankton of the troi)icftI and subtropical Pacific, do not 

 belong with this group becau.se of t heir watery structure and should be classed 

 with the noti-nutritlous forms. 



