28 
F. subquadrata from an unusual bed of inter- 
tidal M. modiolus. About 18% of the mussels 
removed from this area (located at Ten Mile 
Point, Victoria, Vancouver Island, British Col- 
umbia ) are infested. 
DISCUSSION 
F. subquadrata, as do the other two pinno- 
therid species which have been sufficiently 
studied, P. pisum and P. ostreum, has a complex 
postplanktonic life cycle. The anamolous Stage 
I instar is present in the life cycle; and the pre- 
hard and posthard instars, while not identical 
with those of the two species of Pinnotheres, 
are quite similar. Also, as was demonstrated by 
Christensen and McDermott (1958:150) for 
P. ostreum, the first true crab stage following 
the megalops is the invasive stage. 
There are extensive differences, however, be- 
tween the subsequent life cycle of F. subquadrata 
and that reported for P. ostreum by the latter 
authors. Present evidence indicates that the Stage 
I male oyster crab must leave its host and seek 
out the female within her host in order to 
copulate. Following copulation the male leaves 
the female and perishes, either in the open 
water or within a secondary host. The results of 
the present study would indicate that copulation 
in F. subquadrata occurs during a freeswimming 
period, the swarming, in which both the male 
and -the female participate. There is no indica- 
tion that the male subsequently perishes. In fact, 
following the swarming period in late May and 
June, males are frequently taken throughout 
the entire summer. Wells and Wells (1961: 
275) have also noted the continued persistence 
of males of Pinnaxodes floridensis following 
copulation. 3 
In addition to the copulatory swarming and 
persistence of the male following swarming, F. 
3 While at present the genus Pinnaxodes is often 
placed in a different subfamily (the Pinnothereliinae) 
from both Pinnotheres and Pabia (which are in the 
subfamily Pinnotherinae) , there is some question as 
to the validity of this arrangement. Rathbun (1918: 
179) states that Pinnaxodes tomentosus ". . . is very 
likely a Pinnotheres.” A thorough study of the life 
history of the members of this genus will possibly 
indicate closer affinities with the subfamily Pinno- 
therinae, including Pinnotheres and Fabia, than with 
PACIFIC SCIENCE, Vol. XX, January 1966 
subquadrata does not, at any stage in its life his- 
tory, engage in the multiple infestations which 
occur during the early stages of P. ostreum. 
While previous investigations (Christensen 
and McDermott, 1958) suggest that swarming 
is not typical of members of the genus Pinno- 
theres, the recent observations of swarming P. 
maculatus would indicate that at least one spe- 
cies of this group takes part in a copulatory 
swarming. It is suggested, therefore, that other 
pinnotherid species should be studied with re- 
gard to their reproductive behavior. This is 
particularly true in view of Sakai’s paper (see 
footnote 2) in which he mentions a swarming 
or migration as being characteristic of the Asi- 
atic pinnotherid, Tritodynamia horvathi. Miyadi 
(1941) has described a benthic community on 
the basis of a large number of pinnixid crabs 
found covering the bottom of certain areas of 
the Ise-wan, Kii Peninsula, Japan. At one station 
he reports that these crabs, Pinnixa rathbuni, 
occur in densities of up to 344l/m 2 . They were 
found associated with several bottom types. 
Since he thought that such a large number of 
crabs cannot occupy a bottom area for an ex- 
tended period of time, he suggested that among 
other reasons, the crabs could be "... in the re- 
productive period.’’ As both Tritodynamia and 
Pinnixa are related in the subfamily Pinno- 
thereliinae it is not improbable that the phe- 
nomenon observed by Miyadi was actually a 
swarming comparable to that observed by Sakai; 
and, in fact, both might be associated with re- 
production. Thorson (1957:518) describes a 
crab community found in the Persian Gulf as 
being a parallel of Miyadi’s community. The for- 
mer community has as a dominant a pinnotherid, 
Xenophthalamus pinnotheroides, which occurs 
in densities of up to 1,500 mature individuals/ 
m 2 . Again, while Thorson suggests that this 
community is stable, it is not impossible that 
the Pinnothereliinae. Members of the latter subfamily, 
investigated in a recent study (Pearce, 1962b) , as 
well as in the recent descriptions (Wells and Wells, 
1961) of the life history and morphology of Pinna- 
xodes floridensis , differ very markedly in their life 
history from both Fabia and Pinnotheres. Sakai 
(1939:582), in his review of the Japanese Brachy- 
rhyncha, placed the genus Pinnaxodes, along with 
Pinnotheres, in the subfamily Pinnotherinae. 
