Larval Development of Emerita rathbunae — Knight 
73 
opment proceeds. The larvae of E. anologa be- 
come progressively larger than those of E. 
rathbunae, and the carapace spines are consider- 
ably shorter in relation to the length of the 
carapace. The posterior margin of the telson of 
E. analoga larvae becomes increasingly pointed 
and triangular between the prominent eighth 
marginal spines, while that of E. rathbunae re- 
mains smoothly rounded. Measurements of the 
first four stages and of the terminal stage of 
larvae of E. analoga are given in Table 2 for 
comparison with equivalent stages of E. rath- 
bunae. The carapace and telson of both species 
in stage IV are shown in Figures 7—10. 
The larvae of Emerita emerita , described by 
Menon (1933), and E. talpoida, described by 
Rees (1959) and Smith (1877), and those of 
E. rathbunae and E. analoga appear to be very 
similar in structure of appendages and in form 
of carapace and telson. The pattern of develop- 
ment may be common for all species through 
stage III, and through stage IV (with specific 
variation in setation) for those species described 
from the plankton. Larvae of E. emerita, and E. 
talpoida apparently pass directly from zoea IV 
to terminal zoea in the plankton. Those of E. 
talpoida in the laboratory and of E. rathbunae 
and E. analoga in both laboratory and field have 
a variable series of intermediate instars be- 
tween stage IV and the terminal zoea in which 
there is progressive growth and setation with- 
out addition of appendages. The zoeal stages 
which appear to be common to all larvae of the 
genus are as follows: 
1. Uropods absent 
a. Lateral spines on carapace absent, 
4 natatory setae on 
maxillipeds Stage I 
b. Lateral spines on carapace present, 
6 natatory setae on 
maxillipeds Stage II 
2. Uropods present 
a. Pleopods absent, 8 natatory setae 
on maxillipeds Stage III 
b. Pleopods absent, 10 natatory setae 
on maxillipeds Stage IV 
c. Pleopods present, 12 or more 
natatory setae on 
maxillipeds Terminal Stage 
Distribution of Larvae 
The locations of zooplankton samples exam- 
ined and the distribution of Emerita larvae are 
given in Figure 47. Larvae of E. analoga were 
found in samples taken near Magdalena Bay, 
and those of E. rathbunae usually in samples 
taken south and east of Cape San Lucas. A 
group of stage I larvae were found in near- 
shore samples from the west coast of Baja 
California below Magdalena Bay. From mea- 
surements, they appeared to be larvae of E. 
rathbunae, but lack of morphological features 
with which to differentiate stage I larvae of the 
two species makes identification tentative. In 
addition, 16 larvae of E. rathbunae, ranging 
from zoea II to terminal zoea VI, were found 
just south of Magdalena Bay. It seems likely, 
inasmuch as the range of developmental stages 
was found in the sample, that the larvae were 
hatched locally and that populations of the spe- 
cies might be found in the sandy beaches be- 
tween Cape San Lucas and Magdalena Bay. 
Twenty larvae were found in samples taken 
in November and December in the Gulf of 
California, the majority north of La Paz, which, 
although slightly smaller, were almost identical 
with those of the coastal E. analoga in morpho- 
logical detail and proportions. Only late stages 
were obtained. These showed variation in seta- 
tion and development of appendages similar to 
that found in larvae of E. analoga. During Au- 
gust to December, the movements of surface 
water along the western coast of Baja California 
are predominantly offshore and westerly 
(Wyrtki, 1965). It therefore seems unlikely 
that the larvae could have been carried into the 
Gulf from breeding populations near Magda- 
lena Bay. The appearance of the analoga- like 
larvae in a series of samples suggests that either 
Emerita analoga or a closely related species may 
be found in the warm temperate zone of the 
Gulf of California, extending north from Aqua 
Verde Bay on the west coast and Puerto San 
Carlos on the east (Garth, 1955, I960). 
DISCUSSION 
This study of planktonic and cultured larvae 
of Emerita rathbunae has shown that the num- 
ber of zoeal stages in the larval period is vari- 
