88 
response rate as well as a differential behavior 
response. The temperature threshold at which 
the type of response, increased or decreased 
locomotion, and the rate at which the response 
takes place is approximately 17°C for P. car - 
melensis accustomed to an ambient water tem- 
perature of 13°-14°C. A possible explanation 
for this is that accelerated locomotion results 
from a direct influence by the ambient tempera- 
ture on body processes, and decreased locomo- 
tion results as a secondary effect of temperature- 
related factors, such as the reduced availability 
of oxygen as the ambient water temperature in- 
creases. Polychoerus obtains oxygen from the 
aquatic environment by diffusion through epi- 
dermal tissues. The physical characteristics of 
this species are such that sufficient oxygen for 
metabolic processes should be available from 
the environment at the higher temperature 
levels tested if the entire surface of the animal 
is effectively exposed to the environment. How- 
ever, it is possible that little oxygen diffuses 
through the ventral epidermal tissues because of 
the close proximity of the animal to the surface 
on which it crawls. This would reduce by nearly 
one-half the effective diffusion surface and is a 
possible explanation for the curled position re- 
sulting from elevated temperatures in that this 
position exposes about one-half of the ventral 
epidermal tissue to the oxygen-bearing environ- 
ment. 
Locomotion of P. carmelensis at temperatures 
from 8° to 25 °C inclusive takes place in the 
typical flatworm-type posture. The highest in- 
dividual rate of locomotion obtained during 
these tests (2.08) was noted from a worm 
tested at 17°C. The lowest average locomotion 
rate in this temperature range was 0.75 at 8°C, 
and the highest average of 1.50 occurred at 
17°C. These locomotion rates are expressed in 
mm/sec and were measured at a light intensity 
of 60 ft-c. They compare closely with the loco- 
motion rates reported by Armitage (1961) of 
0.86 mm/sec and 1.34 mm/sec measured at 
illumination levels of 6 and 37 ft-c, respec- 
tively. However, he states that the behavior of 
Polychoerus was highly erratic during his loco- 
motion rate tests, in that some individuals spent 
considerable time turning the head from side to 
side and others ceased crawling before reaching 
the end of a 5 -cm course. A possible explana- 
PACIFIC SCIENCE, Vol. XXI, January 1967 
tion of this erratic activity, based on the tem- 
perature-locomotion rate relationship obtained 
in my experiments, is that the water in the petri 
dish used by Armitage in his tests became 
warm during the course of the observations be- 
cause of warm room temperature and/or heat 
from the light source used to stimulate locomo- 
tion. In the present tests, none of the 120 
worms tested between 8° and 25 °C showed 
such behavioral responses. However, several of 
those tested at 29 °C and essentially all at 33°C 
reacted in the erratic manner described by Armi- 
tage. 
Survival Value of Temperature-Locomotion 
Relationship 
According to Armitage (1961), P. carmelen- 
sis does not possess a persistent diurnal rhythm. 
Therefore, this species must depend on an en- 
vironmental "cue” or a combination of such 
environmental stimuli to regulate its daily ac- 
tivity pattern. Observations by Armitage indi- 
cate that light intensity and water turbulence 
play a pronounced role in the regulation of ac- 
tivity and behavior of this animal. Because of j 
the pronounced influence on the velocity of 
movement resulting from slight changes in the i 
ambient water temperature, it seems reasonable 
that temperature and temperature-related factors 
may also function as stimuli regulating activity 
and behavior. 
Armitage postulates that on bright days the | 
absence of Polychoerus from the upper surface 
of rocks and gravel during low tide and rela- 
tively calm water is caused by an increased i 
negative phototropic response to high light in- j 
tensity. However, on April 29, 1965, a cool 
but very bright day with morning sea water at ! 
about 15°C, I observed Polychoerus active on 
the upper surfaces of rocks and gravel through- 
out the period of low tide. This observation, 
made at the same location but earlier in the 
season than that by Armitage, documents the 
fact that high light intensity does not always 
cause a negative phototropic response, and sug- 
gests that there is more than a single factor 
regulating this behavior. Ambient water tem- 
peratures above 17°C cause a reduction in the 
rate of locomotion for animals conditioned to 
13°-l4°C. It is likely that this reduced rate of 
locomotion in response to such temperatures or 
