Polychoerus carmelensis and Temperature Changes — Schwab 
89 
temperature-related factors corresponds to a 
less suitable ambient environment, and that such 
conditions in their natural environment may 
cause P. carmelensis to vacate the upper sur- 
faces of rocks and gravel. 
In my experiments Polychoerus specimens 
were totally incapacitated soon after exposure 
to ambient water temperatures above 29 °C. It 
is reasonable to assume that environmental fac- 
tors would trigger a behavioral escape mechan- 
ism should such temperatures occur in their 
natural habitat. The survival value of such an 
environmental stimulus or combination of stim- 
uli is dependent upon the sensitivity and re- 
sponse of the animal to this factor or factors. 
Armitage reports a 55% increase in rate of 
crawling when the light intensity was increased 
640%, and that in his tests P. carmelensis was 
negatively phototropic. Although the magnitude 
of the light intensity change (in ft-c or in per- 
cent increase) and the sensitivity of the animals 
in terms of response to this factor (rate of 
crawling in mm/sec or percent increase) cannot 
be directly compared to similar calculations 
with respect to temperature change and asso- 
ciated activity response, it seems certain that 
Polychoerus is at least as sensitive to ambient 
water temperature as it is to light intensity. 
Costello and Costello (1938) indicate that 
P. carmelensis may be positively phototropic 
in that individuals showed a tendency to group 
on the moderately lighted side of an aquarium. 
Therefore, there is evidence of both positive 
and negative phototropic response for this spe- 
cies. Armitage suggested that this species may 
have a differential response to low and high 
light intensities. Whether such a light sensi- 
tivity threshold exists, or whether the behavioral 
evidence supporting this possibility results from 
a water temperature-light intensity relationship, 
is at present unknown. 
The physical properties of water are such that 
the heat energy associated with even relatively 
high light intensities may have little immediate 
effect on the temperature of the tide pool. Con- 
versely, tide pool temperatures may in time be- 
come elevated on overcast days with relatively 
low light intensities. Thus, it is possible that 
the absence of this species from tide pools on 
bright days as observed by Armitage may be at 
least in part the result of an elevated ambient 
water temperature associated with high insola- 
tion, rather than the result of high illumination 
levels as a discrete factor. Regardless of the 
nature of causative stimuli, the rate of locomo- 
tion between 8° and 29°C is sufficient for 
Polychoerus to seek a more desirable situation 
under rocks and gravel should the tide pool 
environment warrant such behavior. 
Environment-Induced Posture Responses 
The U-shaped posture resulting from low, 
high, and often from moderately high ambient 
water temperatures appears to be the same 
posture described by Armitage for Polychoerus 
exposed to osmotically unsuitable salinity con- 
centrations. Apparently this species has only the 
U-shaped posture response to both hypo- and 
hypertonic sea water, since Armitage does not 
mention other postures such as the curled pos- 
ture observed in my experiments at certain 
elevated water temperatures. 
During my experiments the U-shaped pos- 
ture often occurred as a response to a gentle 
mechanical stimulus from contact with a soft- 
bristled brush used to transfer the animals from 
one container to another. The fact that this 
posture occurs as a result of temperature change, 
salinity change, and mechanical stimulus sug- 
gests that this posture is a characteristic behav- 
ior response to many undesirable environmental 
conditions. 
Further experimentation may show that the 
curled posture also occurs as a response to a 
variety of stimuli. However, it is certain that 
this response is clearly associated with ambient 
water temperatures near the upper lethal level. 
It is not known if the curled-posture response 
occurs as a direct result of temperature percep- 
tion by a discrete thermoreceptive mechanism or 
as a characteristic response to temperature- 
related environmental factors. It may be that the 
curled posture common at 29°C functions to 
increase the amount of surface area in direct 
contact with the aquatic environment, thus facili- 
tating gaseous exchange, while enabling the 
animal to take shelter. The U-shaped posture 
exposes even more surface area but has no ob- 
vious survival value at temperatures above 
29 °C, inasmuch as the locomotion rate is low 
and the animal soon dies. However, this con- 
clusion is hypothetical, since possible advan- 
