Lepeophtheirus dissimulatus — Lewis 
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Fig. 6. Greatest length of genital segment of de- 
velopmental stages of L. dissimulatus. co, Copepo- 
dite; ch, chalimus; +, measurement includes both 
genital segment and abdomen (one segment in early 
stages). 
comes sporadic, stopping at times and then 
becoming vigorous. During one of the vigorous 
periods of movement a crack appears in the 
anterior dorsal portion of the cuticle and the 
copepodite wriggles out in the same manner as 
in the previous moult. 
The change from the second nauplius to the 
copepodite is the greatest change that occurs in 
a single moult during development. In one 
moult the body is divided from an externally 
unsegmented structure into a cephalothorax con- 
sisting of the head, maxilliped-bearing segment, 
and first pedigerous segment. Further, four free 
segments are visible posterior to the cephalo- 
thorax. The first of these segments bears the 
second thoracic legs, the second bears a pair of 
posteriorly directed spines that may be the pred- 
ecessors of the third thoracic legs, the third free 
segment is naked but will later give rise to the 
fourth thoracic legs, and the fourth free seg- 
ment, to which the caudal rami are attached, 
will later differentiate into the genital segment 
and abdomen. 
Not only does the body break up from a rela- 
tively undifferentiated second nauplius to a co- 
pepodite with a composition comparable to 
that of the adult, but also most of the append- 
ages and processes are now present. Besides the 
antennules, second antennae, and mandibles that 
were present on the first and second nauplius, 
the postoral processes, maxillae, maxillipeds, 
and first two pairs of thoracic legs have been 
added and the caudal rami are now present. 
The general shape of the copepodite body 
(Fig. 8/) is ovoid in both dorsal and lateral 
aspects. The greatest width, that of the cephalo- 
thorax, is less than one-half the greatest length 
(Fig. 5). The anterior cephalothoracic margin 
is sharply convex and the lateral margins are 
flatly convex. A pair of V-shaped indentations, 
or sinuses, are visible in the posterior lateral 
margin of the cephalothorax. These posterior 
sinuses are found at the junction of the posterior 
surfaces of the median and lateral cephalotho- 
racic areas and suggest that the lateral areas are 
distinct from the median and are an outgrowth 
of the cephalon. This is further indicated by 
the longitudinal cephalothoracic grooves which, 
in the copepodite, run anteriorly for a very short 
distance from the apex of the posterior sinuses. 
The median cephalothoracic area does not ex- 
tend past the posterior lateral area and its pos- 
terior margin is irregular. The eyes are distinct 
and similar to those of the naupliar stages. 
The free second pedigerous segment is wider 
than long, its greatest width being 1.3 times the 
length. Both the anterior and posterior margins 
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Time in Hours 
Fig. 7. Greatest width of genital segment of de- 
velopmental stages of L. dissimulatus. co, Copepodite; 
ch, chalimus. 
