FISHERY BULLETIN: VOL. 72. NO. 1 



MATERIALS AND METHODS 



Materials 



Plankton samples examined for the genus 

 Pnntdlitta in the course of this study were ob- 

 tained from three major sources: the zooplankton 

 collections of Scripps Institution of Oceanog- 

 raphy. R. Scheltema's collection of Atlantic 

 zooplankton maintained at the Woods Hole 

 Oceanographic Institution, and quantitative 

 sortings of Pontelliiia from the International 

 Indian Ocean Expedition plankton collections, 

 processed and furnished by the Indian Ocean 

 Biological Centre, Cochin, India. Additional 

 collections or specimens were obtained with 

 the kind cooperation of the National Marine 

 Fisheries Service; the U.S. Naval Oceanographic 

 Office; T. K. S. Bjornberg, University of Sao 

 Paulo, Brazil; A. DeDecker, Division of Sea 

 Fisheries, Cape Town, Republic of South 

 Africa; B. Kimor, Israel Oceanographic and 

 Limnological Research Ltd., Haifa, Israel; 

 J. E. H. Legare, Instituto Oceanografico, Cu- 

 mana, Venezuela; D. J. Tranter, CSIRO, Cron- 

 ulla, Australia. 



Geographical distribution of the samples is 

 shown in Figure la, and the localities yielding 

 Pontellina are listed by species in Table 1. These 

 collections broadly outline most major sectors 

 of the Pacific, Indian, and Atlantic Oceans, the 

 South Atlantic being the notable omission. 

 Most of the samples were taken with open con- 

 ical plankton nets V2 to 1 m in diameter at the 

 mouth. Nets were towed obliquely, vertically, 

 or horizontally between the surface and 200 m 

 of depth. Stations were occupied irrespective of 

 time of day or cloud cover. 



Sample Analysis 



Plankton samples were examined in rect- 

 angular plastic trays (5 X 7.5 X 1 cm) at 16 X 

 magnification with the aid of a stereomicro- 

 scope. The entire sample was scanned if the 

 settling volume did not exceed 20 cc. Otherwise 

 volumetric subsamples were drawn, generally 

 with the aid of a 10-cc piston pipette, after stan- 

 dardizing the total volume and stirring vigorous- 

 ly. Usually more than 2% of the total sample 

 was examined, the actual percentage varying 

 inversely with the size of the original sample. 



Estimates of abundance and frequency of 



occurrence were obtained from particular 

 sets of quantitative samples (Figure lb) selected 

 for homogeneity of sampling. In the case of 

 Pacific zooplankton samples collecting proce- 

 dures followed standard CalCOFI (California 

 Cooperative Oceanic Fisheries Investigations) 

 sampling practices (cf. Smith, 1971). The Indian 

 Ocean samples (Figure lb) are a composite of 

 quantitative Indian Ocean Standard Net tows 

 (Currie, 1963) obtained by various participants 

 in the International Indian Ocean Expedition. 

 Preliminary quantitative processing of these 

 samples was carried out by the Indian Ocean 

 Biological Centre, Cochin, India (Tranter, 

 1969). The Centre provided us with specimens 

 of PontelUua sorted from known fractions of 

 the original samples. Standard quantitative 

 sampling from the Atlantic Ocean was unavail- 

 able to us. 



Specimen Analysis 



For routine examinations specimens were 

 mounted loosely in a drop of glycerol. To en- 

 hance examination of fine denticles and spines, 

 soft tissue was removed by warming specimens 

 in a 10% aqueous solution of KOH at about 

 90 °C for 1 to 2 h. After a brief rinse in distilled 

 water the cuticle was transferred to 35% ethanol, 

 then to 70% ethanol for 1 min and then stained 

 in a solution of 1% Chlorazol Black E dissolved 

 in 70% ethanol. Intensive staining usually re- 

 quires not more than V2 min and should be fol- 

 lowed immediately by a 1-min rinse in distilled 

 water. 



Examinations and dissections were carried 

 out under stereomicroscopes at 12 X to 100 X 

 magnification and under compound micro- 

 scopes at various magnifications up to 600 X . 

 All drawings were made with the aid of a 

 compound microscope equipped with a drawing 

 attachment. 



Several females and males of each species 

 were studied under a scanning electron micro- 

 scope after preparation by the critical point 

 drying method (Cohen, Marlow, and Garner, 

 1968). 



Measurements 



For each species intact specimens with a 

 reasonably straight urosome were chosen at 

 random from localities scattered over the entire 



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