4 
PACIFIC SCIENCE, Vol. XX, January 1966 
represents the most comprehensive study of this 
or any other species of the Pinnotheridae. 
Except for purely taxonomic studies, these 
papers are the main reports concerning the pin- 
notherids despite Rathbun’s (1918:10) early 
admonishment concerning the lack of knowl- 
edge of this family and the inherent rewards to 
be found in its study. 
Other than Wells’ data (1928, 1940) there 
have been no extensive reports concerning the 
biology of F. subquadrata. It is, therefore, one 
of the least studied species of the Pinnotheridae. 
Until Wells’ work of 1928 the male of the spe- 
cies had not been recognized and was, in fact, 
described as a separate species in a different 
genus, Pinnotheres concharum. 
The present paper is concerned with the bi- 
ology of this neglected species. The principal 
study was conducted over a period of one and 
one-half years, from June, 1958 to January, 
I960, but many observations made subsequent 
to the main investigation have been incorpo- 
rated in this paper. Information on the develop- 
mental cycle, reproductive biology, relationship 
to the host organism, distribution and size in 
relation to water depth, and ecdysis is reported 
here. 
The author is especially indebted to Dr. Dixy 
L. Ray, as well as to Dr. Robert Fernald, Dr. 
Ernst Florey, and Dr. Paul Illg, whose valuable 
assistance and helpful criticisms were most use- 
ful in the preparation of this paper. The many 
valuable suggestions of Dr. J. F. L. Hart of Vic- 
toria, British Columbia, and the critical reading 
of the manuscript by A. M. Christensen are also 
acknowledged. 
Finally, I should like to acknowledge the sum- 
mer cooperative fellowship provided me by the 
National Science Foundation in 1959, the Na- 
tional Institutes of Health predoctoral fellow- 
ship (GF 10,872) awarded me during the years 
I960 through 1962, and the NIH postdoctoral 
fellowship (GPD-10, 872-C3) given for study 
at the University of Copenhagen’s Marine Lab- 
oratory, Helsing0r, Denmark. 
MATERIALS AND METHODS 
All field work involved in this study was car- 
ried out at the Marine Laboratory of the Uni- 
versity of Washington, Friday Harbor, San Juan 
Island, Washington. Observations were made on 
the contents of host mussels collected at least 
once but frequently twice per month throughout 
the period of study. In addition, materials were 
collected once a week during the summer 
of June, July, and August of 1958 and 1959. A 
total of 3,480 host mussels were examined dur- 
ing this period. 
The mussels were collected by dredging in 
localities where they are known to occur. The 
dredging gear included either a standard rock 
dredge or beam trawl, depending upon the type 
of bottom from which the mussels were to be 
removed. 
Several areas within the San Juan Archi- 
pelago, selected as dredging sites, were chosen 
as being representative of a variety of depths 
and bottom types. The deepest stations were 
located in President Channel northwest of Orcas 
Island (48°39 / 45"N, 123 0 l'W ), where the wa- 
ter is 195 m in depth. The shallowest station is 
off Point Lawrence, Orcas Island (48°39'30"N, 
122°44 / 45' / W), where the water is 22-30 m 
in depth. Other stations were located near Point 
Caution, San Juan Island (48°34'N, 123°0'48" 
W) in water 130 m in depth; off Mineral Point, 
San Juan Island (48°35'10"N, 123°3'35" W) 
in waters 55 and 130 m deep; and in East Pea 
Vine Pass (48°35'30"N, 122°47'30"W) in 48 
m of water. 
Upon being brought to the surface the mus- 
sels were immediately placed in live boxes with 
circulating sea water. The drains of these boxes 
are covered with screening of a gauge sufficient 
to insure that any swimming stage crabs would 
be retained should they leave their hosts. The 
mussels were then brought into the laboratory 
where they were opened and examined alive for 
the presence of crabs. In those mussels that were 
infested, any damage which may have occurred 
as a result of a crab’s presence was noted. A 
dissecting microscope was always used in these 
examinations. Each mussel was measured, the 
larger ones (greater than 10 mm in length) 
with a vernier caliper, the smaller with a dial 
caliper. The larger mussels were measured to 
the nearest 0.5 mm, the smaller (less than 10 
mm) to 0.1 mm. All crabs collected after July 
15, 1958 were measured with an ocular microm- 
