Biology of Pachygrapsus crassipes —HlATT 
Intimate association between P. crassipes and 
H. oregonensis was rarely observed along the 
outer coast, but was frequently observed in bays 
and estuaries. Here, as in the association with 
H. nudus, the propinquity of the species was 
primarily for purposes of concealment in a 
habitat which provided a minimum of refuge 
places. In the third biotope (see p. 142) both 
species occupied adjacent holes in the muddy 
bank. On several occasions individuals of H. 
oregonensis were observed to enter holes con¬ 
cealing P. crassipes. The hasty departure of the 
former indicated that the two species rarely, if 
ever, concealed themselves within the same 
hole. Moreover, the holes which contained P. 
crassipes were found to have only a single 
occupant; those which concealed H. oregonensis 
often sheltered from one to three individuals. 
Both P. crassipes and the porcellanid crab 
Petrolisthes cinctipes Randall are found under 
rocks of the upper and middle tidal zones. 
Undoubtedly, the concealing habits of both 
species are responsible for their association 
inasmuch as no specific, competitive interrela¬ 
tionship has ever been recorded. There can be 
no competition for food because P. cinctipes is 
a plankton feeder (MacGinitie, 1937). Associa¬ 
tions between P. crassipes and several other lit¬ 
toral types have been discussed elsewhere in 
this paper. 
Precocious Young 
The extraordinary display of activity shown 
by young individuals of this species is suffici¬ 
ently outstanding to merit special attention. 
The young of many cursorial and defenseless 
ungulate mammals are able to run within a 
short time subsequent to birth, have the legs 
developed out of all proportion to the body, 
and usually exhibit mental precocity to a 
marked degree. Similarly, the immature indi¬ 
viduals of P. crassipes are able to attain com¬ 
paratively great speed, have the legs relatively 
longer than the adults, and likewise exhibit 
a high degree of alertness. Although this species 
is confined to a lower littoral stratum than are 
the true land crabs, which exhibit all these 
185 
characters on a more highly evolved level 
(Pearse, 1912, 1914; Cott, 1929), the long 
periods of exposure of P. crassipes seem to have 
provided sufficient stimuli for the manifesta¬ 
tion of those faculties ordinarily associated with 
animals in less protected habitats. The eyes 
of young crabs seem to be comparatively larger, 
and the legs appear to be relatively longer than 
those of adult crabs. In order to check these 
characters, crabs of representative carapace 
lengths (measured from the front to the pos¬ 
terior border), from the first crab stage to the 
largest individual, were selected, and measure¬ 
ments of the long, second ambulatory leg and 
the greatest length of the faceted surface of 
the eye were recorded. The length of the eye 
was measured along the greatest (longitudinal) 
length of the faceted surface and does not in¬ 
clude the eyestalk and terminal style. From 
these measurements ratios were computed be¬ 
tween the length of these structures and the 
carapace. These data are set forth in Table 4. 
TABLE 4 
Ratios between the Length of the Second 
Walking Leg and Length of Faceted Eye-Sur¬ 
face to Length of the Carapace of Several 
Individuals of P. crassipes Ranging from 3.3 to 
38.3 Millimeters in Carapace Length. (Meas¬ 
urements in Mm.) 
CARAPACE 
SECOND WALK¬ 
ING LEG 
EYE 
x 
43 
8 
t 
c 
•5 
6JQ 
6 
x ’S 
1-2 s 
o «j 
bjn u 
X 
& 
r- X 
3-2 8 
<-4-c O CX, 
swO 
1-4 
CQ 
3 
3 
«oo 
X 
J3 
MOO 
3.7 
3.3 
5.0 
1.82 
0.7 6 
0.23 
9.1 
7.6 
13.3 
1.75 
1.3 
.17 
15.2 
13.4 
24.2 
1.80 
1.7 
.13 
20.5 
17.8 
30.6 
1.71 
1.9 
.11 
24.0 
21.0 
35.0 
1.66 
2.1 
.10 
31.1 
25.9 
43.6 
1.68 
2.4 
.09 
37.6 
31.7 
50.4 
1.58 
2.5 
.08 
45.8 
38.3 
61.0 
1.59 
2.8 
0.07 
It is apparent, by reference to columns 4 and 
6 that the length of the second pereiopod and 
of the faceted surface of the eye, respectively, 
as compared with the length of the carapace, 
