68 
(Fig. 27) has 43-55 plumose setae along the 
outer margin. 
The exopodites of the first and second maxil- 
lipeds now bear 14 plumose natatory setae. 
The third maxilliped and thoracic legs (Fig. 
30) have increased greatly in size; the fifth leg, 
curved up and behind the first four, is slightly 
bifid at the tip. 
Now each of the segments 2, 3, 4, and 5 of 
the abdomen bears a pair of uniramous, un- 
segmented pleopods. 
The exopodites of the uropods (Fig. 35) 
bear 7 or 8 setae of varying lengths; twice as 
many larvae had 7 as had 8 setae; a few had 
both 7 and 8 setae. The endopodites are quite 
long, usually 3/4 the length of the exopodites. 
alternate zoeal stages: Of the larvae of 
Emerita rathbunae studied from preserved sam- 
ples, 49 had at least 14 setae on the exopodites 
of the first and second maxillipeds. While 33 
of these larvae were in the described stage VI, 
with pleopods on abdominal somites, and were, 
in many cases, close to molting to megalopa, 
sixteen of the larvae seemed to have prolonged 
the larval cycle to seven zoeal stages. Five 
larvae with 14 natatory setae on the maxillipeds 
did not have pleopods on abdominal segments. 
They had only 6 setae on the exopodites of the 
uropods, 3 tiers of aesthetes on the first antenna, 
and in all other respects (measurements, de- 
velopment of appendages, etc.) were inter- 
PACIFIC SCIENCE, Vol. XXI, January 1967 
mediate between the forms described as zoea V 
and zoea VI. The remaining 11 larvae had 16 
setae on the exopodites of the maxillipeds (one 
had only 15), had pleopods on abdominal 
somites, and were slightly larger and more 
advanced than the form described as zoea VI. 
Two zoea IV and two zoea V were found 
which corresponded with the described stages 
in over-all proportions and in setation. They 
were slightly smaller, however, and some ap- 
pendages were somewhat less developed (flagel- 
lum of second antenna and thoracic legs), 
which suggests that they might be the early 
stages of such an extended larval cycle. 
The variation in development and setation 
of some appendages of cultured larvae within 
stage VI is summarized in Table 3. 
megalopa (Fig. 36) : The megalopa is color- 
less, slightly translucid and very much like the 
adult in form. The most noticeable differences 
are presence of setose pleopods on abdominal 
segments and relatively large eyes. The aver- 
age size of carapace in reared individuals was: 
length, 2.65 mm; width, 1.98 mm. No speci- 
mens from the plankton were available. 
The first antenna (Fig. 37) consists of a 3- 
segmented peduncle and a flagellum. The sec- 
ond and third segments of the peduncle have 
small ventral processes armed with setae and 
that of the third segment is 2-segmented. The 
flagellum usually consists of 10 segments armed 
TABLE 3 
Comparison of Some Features of Cultured Larvae in Stage VI 
from Series with 7, 8, and 9 Zoeal Stages 
HATCHED LARVAE 
PLANKTONIC LARVA 
FEATURE 
7 stages 
8 STAGES 
9 STAGES 
8 STAGES 
First antenna: 
range 
2 
1-2 
1-2 
No. of subterminal 
tiers of aesthetes 
majority 
2 
2 
1 and 2 
3 
Second antenna: 
rudiment to 
Development of flagellum 
range 
= spines 
— spines 0 
to rudiment 
in relation to spines on 
protopodite 
majority 
= spines 
r= j spines 
0 
= spines 
First and second 
range 
13-14 
11-14 
12-14 
maxillipeds: 
majority 
14 
13 and 14 
12 and 13 
14 
Natatory setae 
Uropods: Exopod setae 
range 
6-7 
5-7 
5-7 
majority 
6 
6 
6 
6 and 7 
