Biology of Pachygrapsus crassipes — HIATT 
165 
are then required for the changes undergone 
during period D. A minimum total intermolt 
interval of 65 to 70 days is therefore required 
for the breeding females. Non-ovigerous cap¬ 
tives of similar size require an interval of but 
40 to 50 days. This delayed intermolt interval 
of ovigerous females, coupled with the fact 
that exuvial incidence as well as spawning fre¬ 
quency is highest at this season, indicates that 
the usual temporal sequence of ecdysis is inter¬ 
rupted to such an extent that the total number 
of expected molts is decreased by one each year 
subsequent to maturity. 
On the basis of the data set forth in Figure 9 
it is possible to calculate the number of inter¬ 
molt intervals which will occur in crabs from 
3.4 millimeters or more in initial width to the 
maximal adult size. For example, let us assume 
the initial width of a given crab to be 5.5 milli¬ 
meters. By placing a line along the ordinate of 
the 5.5-millimeter point, it will be found that 
the growth curve will be intersected at a point 
which corresponds to 6.6 millimeters on the 
abscissa. Then, assuming the latter width to 
be the next initial width, the corresponding 
post-exuvial width (8.0 millimeters) may be 
similarly located. The growth curve, therefore, 
enables one to calculate the entire sequence of 
molts from the first crab stage to the termina¬ 
tion of growth. The calculated size increments 
based on the curves shown in Figure 9 check 
accurately with the size increments of wild 
crabs which underwent ecdysis in the field. The 
post-exuvial size increments of recently molted 
wild crabs in representative size categories pro¬ 
vide the following data which closely adhere 
to the expected size increments as calculated 
from the growth curve: small crabs of undeter¬ 
mined sex increased in size from 4.8 to 5.8 
millimeters; male crabs increased from 19.7 
to 22.6 millimeters, and from 33.6 to 37.4 milli¬ 
meters; and female crabs increased from 7.7 
to 9.0, 21.0 to 24.0, and 30.0 to 32.4 millimeters. 
Calculations made in the manner outlined 
above demonstrate that females with an initial 
width of 3.4 millimeters undergo 21 additional 
molts before attaining maximal size, as con¬ 
trasted to 18 for males of corresponding initial 
width. These data are presented together with 
other pertinent data in Table 3. The growth 
curve for females, presented in Figure 10, takes 
into account the fact that female crabs appar¬ 
ently undergo a greater total of molts than do 
males. The curves, of course, represent an 
estimation of the number of molts. Further¬ 
more, it is apparent from the discussion above 
that considerable individual variation may and 
does present itself; nevertheless, on a basis 
of the recorded observations, the curves indicate 
the type of growth that characterizes this species. 
Age 
The interval between hatching and the attain¬ 
ment of the adult or true crab stage must be 
known in order to present accurately an age- 
size scale. It was impossible to determine this 
span for P. crassipes because of laboratory 
deficiencies. However, Hart (1935) investigated 
the larval development of Hemigrapsus nudus 
and H. oregonensis, and the intervals given for 
these two near relatives probably approximate 
the corresponding developmental interval for 
P. crassipes. Hart described one prezoeal stage, 
five zoeal stages, and one megalopal stage for 
both species of Hemigrapsus. Moreover, it was 
shown that the larval stages of the congeners 
were virtually identical both in structure and 
in time of development. Therefore, if the larval 
development of P. crassipes is similar to that 
of its two near relatives, seven molts would 
occur in the interval between the emergence 
from the egg and the attainment of the first 
crab stage. These data, coupled with those 
presented in Table 3, indicate that for a male 
to attain the apparent maximal size of 47.0 
millimeters (the largest size recorded for males) 
it must successfully undergo about 25 molts; 
a female, to attain the maximal size of 44.0 
millimeters (the largest size recorded for 
females), must undergo about 28 molts. 
