Larval Development of Emerita rathbunae — Knight 
71 
laterally and ventrally with strong setae. The 
distal 5 segments bear aesthetes between the 
ventral setae. 
The basal segments of the second antenna 
(Fig. 38) are similar to those of the adult. 
The flagellum consists of 23-25 segments each 
bearing 7 processes: 2 long plumose filtering 
setae, 2 strong setae armed with comblike 
spines, and 3 shorter unarmed setae. 
The mandible (Fig. 39) consists of a light 
gnathal lobe and a palp of 2 segments. The 
first segment of the palp has 3, rarely 2, stout 
setae on the lateral margin, and the terminal 
segment bears setae along the medial and ante- 
rior margins. 
The basal endite of the first maxilla (Fig. 
40) is armed with short, stout teeth and numer- 
ous setae; 1 long plumose seta is conspicuous 
on the anterior-outer corner. On the coxal en- 
dite, a series of long setae curve sharply down 
toward the mouth region. The endopod is un- 
segmented and saclike. There is 1 long seta on 
the lateral angle of the protopodite below the 
endopodite. 
The scaphognathite of the second maxilla 
(Fig. 41) has a dense fringe of approximately 
95 setae along the outer margin. The coxal 
endite is now bilobed; the small distal lobe 
bears 1 long seta. The proximal lobe and the 
basal endite bear many setae. The small tri- 
angular endoped is unarmed. 
The anterior portion of the protopodite of 
the first maxilliped (Fig. 42) is produced into 
a flat blade armed with rows of small setae and 
a series of long plumose setae on the basal por- 
tion. The exopodite consists of 2 segments; the 
bladelike terminal segment is fringed with 
plumose setae. The rudimentary endopod is 
unarmed. 
The exopodite of the second maxilliped (Fig. 
43) is 2-segmented; the first segment bears 
3-4 strong setae on the lateral margin and the 
small oval terminal segment is fringed with 
plumose setae. The endopodite consists of 4 
segments with setation as figured. 
The meropodites of the third maxilliped 
(Fig. 44) are broad and opercular. The 3 slen- 
der terminal segments bear plumose and bristle 
setae; the inner surfaces are covered with dense 
rows of setae to form a brushlike structure. 
The pereiopods are like those of the adult 
in form, with the first three pairs directed for- 
ward and the fourth pair directed posteriorly. 
The fifth legs, slender and chelate, are curved 
up beneath the carapace. 
The abdomen now consists of 6 segments; 
segments 2, 3, 4, and 5 bear biramous pleopods 
and segment 6 carries biramous uropods. The 
pleopods (Fig. 45) decrease in length posteri- 
orly. The exopodites bear plumose setae; the 
first pair has 14-15 setae, the second pair bears 
15-16 setae, and the third and fourth pairs 
have 17-18 setae. The knoblike endopodites 
increase in length from the first to the fourth 
pair and have tiny median hooks which inter- 
lock with those of the opposite pleopod to form 
a single swimming unit of the pair. 
The oval exopodites and endopodites of the 
uropods (Fig. 46) are fringed with plumose 
and small unarmed setae. The triangular telson 
(Fig. 46) has plumose setae along the lateral 
margins. 
Comparison of Species 
Among larvae of Emerita analoga studied 
from preserved plankton samples, the early 
stages, I-IV (the "low stage IV” described by 
Johnson and Lewis (1942:79) with usually 
10, occasionally 9 or 11, setae on the first and 
second maxillipeds) , were found to be consis- 
tent in detail and degree of development, but 
later stages showed such variation in setation 
and development of appendages that the num- 
ber of molts through which any individual had 
progressed could not be ascertained with con- 
fidence. The terminal zoeas, with indications 
of postlarval appendages beneath the cuticle, 
were consistent in possession of pleopods, an 
extremely long flagellum on the second antenna, 
and 5 tiers of subterminal aesthetes on the first 
antenna, as described by Johnson and Lewis. 
From 16-19 setae were found on the exopodites 
of the maxillipeds. Groupings of the late stage 
larvae by size and relative growth of appen- 
dages suggested that there were at least 7 zoeal 
instars in the planktonic larval life of the 
species. 
No differences in morphological detail were 
detected between larvae of Emerita rathbunae 
and E. analoga in stages I and II. In stage III, 
the uropods of E. analoga may bear 3 setae but 
7 out of 10 specimens examined had only 2 
