LABORATORY PROCEDURE 



Following procedures defined by Hida and 

 King (1955), a displacement volume measure- 

 ment was obtained for each sample; "group 

 counts" were made on samples from cruises 27 

 and 30 of the Smith and cruises 17 and 18 of the 

 Gilbert . These counts were to major category- 

 only and not to the species level. The relative 

 abundance of the individual species was evaluated 

 in the following manner. The entire plankton 

 sample, or aliquot in the case of large samples, 

 was spread out in a dish, and from about 20 to 

 200 chaetognaths were removed, the number 

 depending upon their abundance in the sample. 

 The different species were identified, segre- 

 gated, and, principally on the basis of our 

 estimate of their absolute numbers in the sample, 

 classified into one of four categories: conspicu- 

 ously abundant, abundant, common, and present. 

 For example, 230 chaetognaths were renaoved 

 from the sample collected at station 8, cruise 

 1 7 of the Charles H. Gilbert; the number of each 

 species and their abundance were classified as 

 follows: 126 Sagitta bipunctata, conspicuously 

 abundant; 66 S. serratodentata, abundant; 22 

 Pterosagitta draco, common; 10 S. hexaptera, 

 common; 5 S. lyra, present; and 1 S. enflata, 

 present. 



Since they sink to the bottom of the 

 collection jar, a representative sample of 

 pteropods was easily obtained by decanting the 

 sample until a rich concentrate of pteropods re- 

 mained which was poured into a small dish, 

 identified, and ranked in the same manner as 

 were the chaetognaths. 



The species distributions were classified 

 into three categories, abundant, common, and 

 present, and are summarized in tables 1 and 2. 

 Since each summary evaluation was based on 

 several, or many, samples the "conspicuously 

 abundant" category was not applicable. 

 Although this method of classification is only 

 partially quantitative, we believe the results 

 are sufficiently precise for the purposes of this 

 study. It is our opinion that detailed species 

 counts would not have made any significant 

 changes in our evaluations. 



Although most of the chaetognaths and 

 pteropods were identified to species, there were 

 a few unidentified forms which have been omitted 

 from this report. Therefore the species listed 

 were not necessarily the only ones present. 



References used in identifying the 

 chaetognaths were Dakin and Colefax (1940), 

 Fowler (1906). Eraser (1952), Germain and 

 Joubin (1916), Michael (1911). and Thomson 

 (1947). For the pteropods the principal author- 

 ity consulted was Tesch (1946, 1948). 



RESULTS 



While there were no obvious east-west 

 differences in the distribution of the chaetog- 

 naths and pteropods, the north-south differ- 

 ences were marked. Three distinct 

 subdivisions or faunal zones were evident from 

 their distribution. The chaetognaths and ptero- 

 pods identified fronneach of the zones are listed 

 in tables 1 and 2. Pteropods were not studied 

 as intensively as chaetognaths because it 



Table 1. --Chaetognaths of the North Pacific and the faunal zones in which they 

 occurred: data from Charles H. Gilbert cruises 17, 18. and 23 

 and Hugh M. Smith cruises 25, 27, and 30 



* = present, ** = common, *** = abundant 



