18 
PACIFIC SCIENCE, VoL XX, January 1966 
tion is supported by the fact that the earlier 
Stage V crabs (found in late summer) are a I- 
ways smaller on an average than are the ovigers 
taken later in the year at the same station and 
depth. 
The only previous study concerning the com- 
plete postplanktonic life cycle of a pinnotherid 
is that made by Christensen and McDermott 
(1958). They found that: (1) the number of 
Stage I P. ostreum was at a minimum during 
the winter and spring months and that in June 
large numbers of Stage I crabs appear in the 
oyster hosts; (2) the Stage I crabs represented, 
during this period, up to 60 % of the total popu- 
lation; (3) 45% of the Stage I crabs were 
males; (4) by the end of July only 5% of the 
crabs collected were males and by early Septem- 
ber not a single male could be found. 
In addition to the ultimate disappearance of 
the males from the P. ostreum population they 
noted that during a period in late June a sig- 
nificant number of double infestations began to 
appear. They suggested that these could only be 
due to new Invasions by male Stage I crabs seek- 
ing copulatory partners within the host oyster. 
In view of this fact, and of the present observa- 
tions that p. subquadrata engages in swarming 
and the male survives through the summer, it 
can only be assumed that P. ostreum and F. sub- 
quadrata have diverged widely in their repro- 
ductive habits. 
It is believed that some female F. subquadrata 
live for more than one year and also reproduce 
more than once. Figure 3 shows that there are 
always residuals of the nondominant stages. For 
instance, in the summer when the Immature in- 
stars ( of all stages ) predominate, there is always 
a percentage of Stage V crabs and occasionally 
an ovigerous female. Since these crabs were fre- 
quently much larger than average ( often greater 
than 12 mm in carapace width) it is thought 
that they are remnants of the previous year’s 
adult population and not merely precociously 
developed individuals of the present year. Chris- 
tensen and McDermott (1958:159) present evi- 
dence that P. ostreum may live as long as three 
years. There can be no doubt, however, that 
some of the smaller, "residual,” Stage V F. sub- 
quadrata are the result of spawnings occurring 
somewhat earlier in the year than the majority 
It is possible that they are the offspring of second 
year females. 
The immature crabs which are found later in 
the season and throughout the winter (Fig. 3),' 
when the Stage Y crabs are predominant, are 
almost certainly the result of the egg deposition 
subsequent to the period when the majority of 
the crabs spawn. Similarly, Stage I males are 
found throughout the winter. Since they too are 
larger than the average Stage I males collected 
during May, when the swarming occurs, it is 
believed that they represent a remnant of the 
male population of the previous summer. 
Atkins (1955:689) has shown that it is pos- 
sible for one implantation of sperm to success- 
fully fertilize a second egg deposition which 
might be produced by a female P. pisum. Chris- 
tensen and McDermott (1958:167) also present 
evidence tending to confirm the same thing in 
P. ostreum , as do Wells and Wells (1961:275) 
in Pinnaxodes floridensis , and Pearce (1962^) 
in Pinnixa jaba and P. littoralis . 
Whether it is possible for a second copula- 
tion to occur in F. subquadrata is extremely 
doubtful. Christensen and McDermott (1958: 
167) report what .might be a copulation be- 
tween a male, Stage I crab and a female, Stage 
V instar of P ostreum. They doubt, however, 
that such a copulation would normally occur in 
this species. If copulation in ,F. subquadrata is 
restricted to the period of swarming in open 
waters it is obvious that, because of its morphol- 
ogy, the Stage Y instar can never leave the host 
and is thus unable to copulate a second time in 
open water. Since no Stage V female has ever 
been noted to be accompanied by a hard stage 
male or, for that matter, a male of any other 
stage, it can probably be assumed that a second 
infestation is not tolerated and it is thus doubt- 
ful that a second copulation would or could oc- 
cur. Furthermore, as was pointed out by Stauber 
(1945:270) for P. ostreum , the size difference 
between the average adult female and the hard 
stage male probably makes copulation mechan- 
ically Impossible. 
GROWTH AND DEVELOPMENT CORRELATED 
WITH HOST SIZE 
Wells (1940:45) found that a definite posi- 
tive correlation could be established between the 
