Lepeophtbeirus dissimulatus — Lewis 
in the third chalimus. The general shape of the 
two antennular segments is similar to that of 
the preceding stage although the two distinct 
swellings present on the distal end of the first 
segment are now absent. The anterior surface 
of the first segment bears 10 setae that are dis- 
tinctly plumose; the anterior distal surface bears 
two plumose setae. The second segment bears 
a single naked seta from the middle of the pos- 
terior margin, four from the posterior distal 
surface, and six from the anterior distal. 
The antennule of the fifth chalimus (Fig. 
14/?) is attached in the same region as that of the 
fourth although the swelling at the junction of 
the appendage and the frontal region is not as 
distinct. The overlap of the antennule base onto 
the anterior ventral surface of the cephalothorax 
(see Fig. 13 e-h) in the fifth and sixth chalimus 
and the adult may be due, at least in part, to 
the incorporation of the swollen portion of the 
frontal region into the frontal region of later 
stages and the resultant displacement of the pos- 
terior portion of the antennule base onto the 
cephalothorax. The attachment of the antennule 
thus appears to be basically on the frontal re- 
gion and secondarily on the cephalothorax. The 
first segment of the fifth chalimus antennule is, 
with regard to the second segment, slightly 
longer than in the preceding stage, being more 
than twice the length of the second segment. 
The greatest width of the segment is slightly 
more than IV 2 times the length; the anterior 
margin is flatly convex medially and broadly 
rounded distally and proximally. The posterior 
margin is irregular, with a slight angular pro- 
trusion from the distal region. The anterior 
surface of the first segment bears 16 plumose 
setae, the distal surface three. The length of the 
second segment is approximately 21/2 times the 
width, the lateral margins are flatly convex, and 
the distal margin is rounded. The armature of 
this segment is the same as in the preceding 
stage. 
The antennule of the sixth chalimus (Fig. 
1 4i) is attached to the ventral lateral surface of 
the frontal region and is adjacent to or slightly 
overlaps the anterior ventral surface of the 
cephalothorax. The second segment is slightly 
longer than that of the preceding stage. The 
first segment is broad proximally, its greatest 
width being approximately five-eighths of the 
215 
greatest length, and tapers to the narrow distal 
end. The anterior margin is irregular except for 
the broadly convex proximal region, the poste- 
rior margin is shorter than the anterior, and the 
posterior surface bears a small distal protrusion. 
Nineteen plumose setae arise from the anterior 
surface of the first segment and the rounded dis- 
tal surface bears five more. The second segment 
is club-shaped; the greatest width is slightly 
more than one-third the length. The lateral mar- 
gins are generally flatly convex, the proximal 
end slightly narrower than the rounded distal 
end. The armature of the second segment con- 
sists of one naked seta from the middle of the 
posterior margin and 11 naked setae from the 
distal surface. 
The antennule of the adult (Fig. 14;) is sim- 
ilar to that of the sixth chalimus except for the 
armature. The first segment has a small bifurcate 
protrusion on the posterior distal corner, the 
spines of which are crenate in the female and 
dentate in the male. The first segment bears 20 
plumose setae on its anterior and distal surfaces; 
the second segment bears one naked seta on the 
middle of the posterior surface and 12 naked 
setae on the distal surface. 
Second Antenna 
In contrast to the antennule, the second an- 
tenna changes drastically during the life cycle 
of L. dissimulatus, from a biramous swimming 
appendage in the nauplius to a uniramous pre- 
hensile appendage in the adult. 
The second antenna of the first nauplius (Fig. 
15^) is biramous and attached to the ventral 
lateral surface just posterior to the base of the 
antennule. The protopodite is one-segmented, 
its greatest width approximately three-fourths 
of the greatest length. The lateral margins, ex- 
cept at the proximal end, are almost parallel; 
the distal margin is broadly curved. The five- 
segmented exopodite arises from the dorsal lat- 
eral surface of the protopodite, not from the 
distal end; the division between the exopodite 
and the protopodite is indistinct and incom- 
plete. The first exopodite segment is slightly 
longer than the second, its proximal region tap- 
ered evenly to the narrow distal end. The second 
segment is tapered evenly from the proximal 
to the narrow distal end; a single lightly plu- 
mose seta is present on the inner distal lateral 
