FISHERY BULLETIN: VOL. 78, NO. 2 



pleopods 2-5. Furcilia IV was separated from fur- 

 cilia V by the segmentation of antennal flagella, 

 maxilliped endopod, and leg 5 endopod; and en- 

 dopod setation of pleopods 2-5, with small overlap 

 on pleopod 3 only. Grouping of stages by terminal 

 telson spine number would not be supported by 

 these characters and if, for instance, all larvae 

 with 1 terminal and 3 pairs posterolateral telson 

 spines were grouped together, the range in size 

 within the stage would become uncomfortably 

 large, more than twice that of furcilia III and al- 

 most twice that in furcilia V. Variability in reduc- 

 tion of posterolateral spines was seen in furcilia VI 

 and rarely in juvenile I. 



The number of telson spines did relate to varia- 

 tion in size within a stage. For instance, furcilia III 

 larvae that would molt from 7 to 3 terminal spines 

 were 0.04 mm smaller on the average than those 

 that would molt from 7 to 1 terminal spine and in 

 furcilia IV, larvae with 3 terminal spines were 

 0.08 mm smaller on the average than those with 1 

 terminal spine. Variation in morphology within a 

 stage was assessed in a sample of larvae from one 

 location, as by midfurcilia phase there was a 

 noticeable difference in rate of development be- 

 tween areas within the range of the population. It 

 may be seen, for example, in a comparison of the 

 length of larval stages at two locations in the 

 California Current terminus (Figure 11) that, al- 

 though they were smaller on the average, furcilia 

 VI larvae from Station 10 in the mouth of the Gulf 

 of California were within the size range of juvenile 

 I of the slower growing larvae from Station 6 off 

 western Baja California. The patterns of telson 

 spine reduction in furcilia III-VI and juvenile I at 

 these two locations, shown in Table 7, exemplify 

 variation within the stages which appears to 

 reflect the difference in rate of growth and mor- 

 phogenesis. 



only in all stages (Figure 12, Table 8); northern 

 form larvae had 2 pairs of lateral telson spines 

 from furcilia V. Furcilia III was slightly more vari- 

 able in number of terminal telson spines while 

 furcilia IV was less variable (Table 1). The 

 carapace differed also with relatively longer pos- 

 terodorsal spines from calyptopis I to furcilia I 

 (Figures 3e-g, 8e) and sometimes with slightly 

 larger and more persistant marginal spines. 



Development of appendages was usually similar 

 in the two forms. The lateral spine of the anten- 

 nule was sometimes shorter and the lappet less 

 developed in southern form furcilia VI and the 

 setation of maxillule basal endite differed: 20, 62, 

 and 75% of larvae examined had acquired 2 setae 

 on the proximal margin of endite in furcilia V, VI, 

 and juvenile I among northern form larvae while 

 only 0, 2, and 17% of southern form larvae had a 

 second seta in these stages. 



Southern form larvae were smaller on the aver- 

 age in the furcilia phase but, as in the California 

 Current terminus, differences in growth per stage 

 between areas within the range of the population 

 were noted. Developmental stages of E. eximia 

 from the Peru Current (Stations 1520/1604) were 

 larger on the average than those from the South 



Table 7. — Pattern of telson spine reduction in furcilia III-VI 

 and juvenile I in the northern form of Euphausia eximia at two 

 locations (Stations 6 and 10) in the California Current terminus. 

 Values indicate percentage with telson armature in stage. 



Terminal + posterolateral telson spines 



Stage Stn 7+3 6+3 5+3 4+3 3+3 2+3 1+3 1+2 n 



Furcilia 6 100.0 — — — — — — — 280 



III 10 97.0 — 15 — 1.5 — — — 68 

 Furcilia 6 — 0.7 2.9 5.1 36.7 21.1 33.5 — 275 



IV 10 — — — — 15.1 190 65.9 — 126 

 Furcilia e — — — — — — 100.0 — 41 



V 10 — — — — — — 100.0 — 97 



Furcilia e — — — — — — 92.9 7.1 14 



VI 10 — — — — — — 21.4 78.6 14 



Juvenile 6 — — — — — — 25.0 750 12 



I 10 — — — — — — — 100.0 24 



South Pacific Population 



Larvae from two areas within the southern 

 range of E. eximia (Figure 1) were compared with 

 larvae from the California Current terminus and, 

 although the populations were generally similar, 

 discrepancies were discovered. The most con- 

 spicuous differences proved to be in the armature 

 of the telson. Among larvae in the South Equato- 

 rial and Peru Current population (southern form), 

 the middle posterolateral spine was longer rela- 

 tive to the other two posterolateral spines and the 

 majority of larvae had one pair of lateral spines 



Table 8. — Number of pairs of lateral telson spines in furcilia 

 TV- VI, juvenile I, and adult in northern and southern forms of 

 Euphausia eximia. Values indicate percentage with telson ar- 

 mature in stage. 



Pairs of lateral telson spines 



328 



