KNIGHT; STAGES OF THYSANOPODA TRICUSPWATA 



pound microscope equipped with drawing at- 

 tachment. 



Nomenclature for description of appendages 

 is based on that of Gurney (1942) . For a review 

 of the literature on larval development of the 

 Euphausiacea and the nomenclature of their 

 larval phases, the reader is referred to the papers 

 by Gopalakrishnan (in press) and by Mauchline 

 and Fisher (1969). 



RESULTS 



DESCRIPTION OF 

 DEVELOPMENTAL STAGES 



Nauplius II (Figure la, b) 



Measurements: TL, r = 1.00-1.12 mm, m = 

 { 1.06 mm; W, r = 0.48-0.56 mm, m = 0.53 mm; 



n = 43. 

 jj Body oval, about 2 times as long as wide, an- 

 ' terior pointed, posterior truncate; posterior 

 margin armed with 10 spines — 3 pairs of pos- 

 terolateral spines and 2 pairs of small to rudi- 

 mentary medial terminal spines, posterolateral 

 i spine 1 (outer) is small, spines 2 and 3 are rel- 

 atively large, only spine 3 (inner) bears spinules. 



Antennule (Figure 4a) uniramous; with 2 

 terminal setae, 1 subterminal seta situated me- 

 dioventrally, and small spiny prominences at 

 base of each seta — that below largest terminal 

 seta is like small lobe; spinules are distributed 

 on surface as figured. 



Antenna (Figure 5a) biramous; protopod 

 may be constricted near middle and appear weak- 

 ly segmented; endopod unsegmented with 3 term- 

 inal plumose setae, a rudiment of 4th terminal 

 seta, 1 subterminal seta on inner margin, and 

 rows of spinules at bases of setae; exopod with 

 outer margin divided into about 10-11 segments 

 (the segmentation was often indistinct in most 

 distal and proximal parts of exopod) , the 5 distal 

 segments bear plumose setae — the terminal seg- 

 ment has 2 setae with a few spinules and the 

 remaining 4 segments bear 1 seta each. 



Mandible (Figure 6a) biramous and unseg- 

 mented ; both rami bear 3 plumose setae with 

 spinules at base of setae. 



In well-developed nauplii nearing molt to 



metanauplius, the carapace of the metanauplius 

 with its distinctive ornamentation could be seen 

 inside the cuticle of the nauplius (Figure la), 

 both the large long spines around the anterior 

 margin which fold up and back around the body 

 and the 4 large medial and smaller posterolateral 

 spines on posterior margin may be visible and 

 may be partially dissected out. 



Metanauplius (Figure Ic, d) 



Measurements: Equatorial Pacific larvae - 

 TL, r = 1.36-1.50 mm, m = 1.43 mm; CL, r = 

 1.02-1.10 mm, m = 1.05 mm; CW, r = 0.60- 

 0.70 mm, m = 0.64 mm; n — 39. Indian Ocean 

 larvae - TL, r = 1.36-1.52 mm, m = 1.45; CL, 

 r = 0.98-1.10 mm, m = 1.05 mm; CW, r = 

 0.61-0.68 mm, m = 0.65, n = 43. 



Carapace with rounded frontal and anterolat- 

 eral margins produced into long spines (the num- 

 ber of spines, counted in 25 individuals, ranged 

 from 21 to 23 with 23 larvae having 22 spines), 

 there may be tiny spines or "hairs" posterior 

 to the posteriorly directed last large spine; pos- 

 terolaterally deep winglike extensions of car- 

 apace curve ventrolaterally with margins pro- 

 duced into strong posteriorly directed spines 

 which diminish in size around posterior margin 

 where they are separated by small spines; the 

 4 large medial spines on posterior margin are 

 usually relatively long and they project up dor- 

 sally away from body of larva. A faint outline 

 of developing eyes is visible. Tail long and taper- 

 ing with rounded posterolateral margins and 

 median indentation, there is now a pair of lat- 

 eral spines in addition to 3 pairs of posterolateral 

 spines and 2 pairs of medial terminal spines, a 

 small rudiment of one or both of inner (third) 

 pair of terminal spines may be present. 



In one well-developed metanauplius near molt, 

 the telson of calyptopis I with invaginated ter- 

 minal and lateral spines was visible beneath the 

 cuticle (Figure le). As can be seen, postero- 

 lateral spine 3, although shorter than spine 2 in 

 the metanauplius, is more deeply invaginated 

 and longer than spine 2 in the developing calyp- 

 topis, and when extruded, it will have the greater 

 relative length observed in the calyptopis stages 

 of T. tricuspidata. 



55 



