GOPALAKRISHNAN: ZOOGEOGRAPHY OF NEMATOSCELIS 



surface. Assuming 0° wire angle the net would be 

 expected to filter approximately 200 m^ of water; 

 but 0° wire angle was rarely attained at sea. 

 Moreover, Tranter and Smith ( 1968) showed that 

 the initial filtering efficiency of this net is 0.96; 

 subsequent clogging does not reduce the filtering 

 volume significantly. 



Plankton samples collected according to these 

 procedures are classified as "standard." In waters 

 over the continental shelf where the depth was 

 less than 200 m, the net was usually hauled up 

 from within a few meters of the bottom; such col- 

 lections were also treated as standard since the 

 full water column was filtered. Samples collected 

 from less than approximately 200-m depth in the 

 open ocean, where the depth was far greater than 

 200 m, were designated as "nonstandard." 



All samples were processed and sorted at the 

 Indian Ocean Biological Centre situated in 

 Cochin, India. The list of plankton samples pro- 



cessed at this center is included in a handbook to 

 the international collections (Indian Ocean 

 Biological Centre, 1969). The locality, time, and 

 depth of haul at each station are given in this list, 

 along with total displacement volume of the sam- 

 ple and fraction of each sample that was sorted 

 into major taxa. At the sorting center a 3- to 4-ml 

 portion of each sample was sorted into its con- 

 stituent major taxa after removing large indi- 

 viduals from the sample. Individuals in each 

 group were then counted to give an estimate of 

 numbers in the whole sample. The sorted fractions 

 ranged from dVc to 907f of the whole sample on the 

 basis of the initial displacement volume of the 

 sample. Further details of the sorting procedure 

 were described by Hansen (1966). The unsorted 

 portion (archive) of all samples were deposited at 

 the Indian Ocean Biological Centre. About 215 of 

 them were examined during the present study in 

 order to check whether the fractionating proce- 



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STATIONS FROM WHICH 

 STANDARD ZOOPLANKTON 



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 DURING OCT 16 -APRIL 15 



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Figure 1. — Plankton samples examined for Nematoscelis of the Indian Ocean: b - NE Monsoon period. 



1041 



