90 
tages of either posture to animals exposed to 
high water temperatures are not known. 
CONCLUSIONS 
1. The ambient water temperature clearly 
influences both the rate and the sign of Poly- 
choerus’ locomotion. A rate-directional response 
threshold was measured at 17°C for animals 
conditioned to 14°C in that, as temperatures 
increased from 5° to 17°, the speed of locomo- 
tion increased from an average of 17.4 to 90.4 
mm/min, at the rate of 6.1 mm/min/°C. Fur- 
ther temperature increases from 17° to 33° C 
caused a steady decrease in locomotion speed 
from an average of 90.4 to 32.8 mm/min, and 
the rate of reduction per degree of temperature 
increase, — 4.4 mm/min, was relatively low. 
2. The highest average speed of locomotion 
(90.4 mm/min) and the greatest individual 
rate (122.5 mm/min) were measured at 17°C, 
which is near the temperature of sea water at 
the location and season at which these experi- 
ments were conducted. This suggests the pos- 
sibility that the maximum locomotion rate is a 
function of the ambient water temperature with 
respect to possible seasonal acclimatization by 
the animal. 
3. It is postulated that the increased rate of 
locomotion as temperatures changed from 5° 
to 17°C corresponds to a general temperature- 
related acceleration of the body processes. It is 
not known why temperature increases above 
17°C cause a reduction of locomotion speed. 
Possibly this is a function of decreased amounts 
of available oxygen due to elevated water 'tem- 
peratures and/or crossing a critical temperature 
threshold for enzymatic action. 
4. Polychoerus has a differential movement 
posture with respect to high and low water 
temperatures. At 5°C this species contracts into 
a U-shaped position, and movement at an aver- 
age rate of 17.4 mm/min results from motion 
of the cilia on the dorsal surface of the animal. 
In ambient sea water temperatures of 29° C and 
PACIFIC SCIENCE, Vol. XXI, January 1967 
above, movement generally occurs while the 
animal is in the usual flatworm position, but 
with the posterior portion of the body drawn | 
up under the more anterior portion. In this po- 
sition the average rate of movement was 50.2 [ 
mm/min at 29°C and 32.8 mm/min at 33°C ! 
5. Sea water temperatures slightly below 
5°C and above 29 °C are not suitable for the 
survival of P. carmelensis conditioned at a 
temperature of about 14°C. However, the rate 
of locomotion at these temperatures appears | 
sufficient to allow this species to avoid such 
conditions should they occur in the tide pool. 
Measurements of temperatures prevailing be- 
neath the rocks and gravel in these tide pools 
is needed. 
6. It is probable that the temperature of | ! 
the ambient sea water, as well as the intensity 
of illumination and the turbulence of water, 
function as an environmental stimulus regulat- ! 
ing the activity and behavior of Polychoerus . 
REFERENCES !; 
Armitage, K. B. 1961. Studies of the biology j 
of Polychoerus carmelensis (Turbellaria: j: 
Acoela). Pacific Sci. 15:203-210. 
Costello, H. M., and D. P. Costello. 1938. 
A new species of Polychoerus from the Pa- 
cific Coast. Ann. Mag. Nat. Hist., Ser. 11, 
1:148-155. 
De Beer, G. R. 1954. The evolution of the 
metazoa. In: Julian Huxley et ah, eds., Evo- ; 
lution as a Process. George Allen and Unwin, 
London. 367 pp. 
Hanson, E. D. 1958. On the origin of the 
Eumetazoa. Systematic Zook 7:16-47. 
Prosser, C. L», and F. A. Brown, Jr. 1961. : : 
Comparative Animal Physiology. 2nd ed. W, 
B. Saunders Co., Philadelphia. 688 pp. 
Ricketts, E. F., and J. Calvin. 1952. Between I 
Pacific Tides. 3rd ed. Rev. by J. W. Hedg- 
peth. Stanford University Press, California. 
502 pp. 
