KNIGHT LARVAL DEVELOPMENT OF EUPHAUSIA EXIMIA 



was carried out on samples of E. eximia from 

 across the species' range. Variation in number of 

 pairs of lateral telson spines was found to persist 

 in the adult (Table 8) and a discrepancy in the 

 armature of antennular peduncle, described and 

 photographed by Roger (1967) in equatorial E. 

 eximia, was found as well. The inner process of 

 antennular peduncle segment 2 had 1 or 2 spines 

 in the northern form and 1-5 spines in southern 

 form adults ( Table 9) and the number of spines was 

 related to size. Northern form adults <21 mm TL 

 had 1 spine only; 1 or 2 spines were found only on 

 the largest animals of 21-27 mm. Southern (ormE. 

 eximia of 12-18 mm length had 1-4 spines but 

 animals >18 mm had 2-5 spines; 1 spine was not 

 seen on the larger adults. Armature of the process 

 was often asymmetrical. 



The differences between populations of E. 

 eximia in frequency of numbers of lateral spine 

 pairs on the telson of furcilia V-VI and adult, and 

 in armature of adult antennular peduncle seg- 

 ment 2 proved highly significant (P = <0.005) in 

 chi-square analyses. 



Table 9. — Number of spines on inner process of antennular 

 peduncle segment 2 in adults of the northern and southern forms 

 ofEuphausia eximia. Values indicate percentage with armature 

 in form. 



Vertical Distribution 



When larvae were sorted for taxonomic study, 

 they were also counted at three stations in day and 

 night series of vertical samples taken during Krill 

 Expedition (Brinton 1979). The data obtained are 

 presented in Tables 10-12. 



At Station 6, west of Baja California in the 

 California Current (Table 10), the distribution of 

 eggs corresponded with the nighttime range of 

 adults indicating that the majority of female E. 

 eximia had spawned in the surface waters during 

 the night. The highest concentration of meta- 

 nauplii was found in the layer below the surface, 

 reflecting sinkingof eggs prior to hatching( Mauch- 

 line and Fisher (1969) note that eggs of Thysan- 

 oessa raschii and Meganyctiphanes norvegica 

 sank at 5.5-7.5 m/h in water of 33.3% and 15° C). 

 The majority of calyptopes and early furcilia 

 stages were in the surface layer during the day, 

 sinking to strata beneath at night. The pattern 

 shifted gradually in midfurcilia phase and from 

 furcilia III, the stage when all pleopods are setose, 

 the larvae moved deeper in the daytime and 

 toward the surface at night, and developed stron- 

 ger migrating capability with increasing size. 



The larval population structure and distribu- 

 tion pattern varied at Station 10 in the mouth of 

 the Gulf of California (Table 11). No eggs were 

 found and larvae were most abundant in early 

 furcilia stages instead of in the metanauplius and 

 calyptopis phases. The metanauplii were seen at 

 the surface, and there was no evidence of nightly 



Table 10. — Vertical distribution (percentage of stage at depth) of larvae and adults of Euphausia eximia in day and night samples 

 from the California Current terminus off western Baja California (Station 6) and number/1,000 m^ in each stage. 



331 



