Studies of the Biology of Polychoerus carmelensis (Turbellaria: Acoela) 
Kenneth B. Armitage 1 
Little is known about the biology of the 
Acoela. Hyman has summarized both earlier 
(1951) and more recent studies (1959: 731 and 
f.). The Acoela are of particular interest because 
typically they lack a gut and lack protonephridia, 
and frequently lack eyes. Thus they carry on a 
number of biological activities without having 
the structural modifications associated with these 
activities. The biology of the Acoela is of fur- 
ther interest because of the hypothesis of Hadzi 
that the Acoela are the stem group of the Eume- 
tazoa and were derived from ciliates (de Beer, 
1954; Hanson, 1958). 
Polychoerus carmelensis is found in the pools 
of the mid-tide horizon in the vicinity of Mon- 
terey, California (Ricketts and Calvin, 1952: 
49 ) . Costello and Costello have described copu- 
lation ( 1938^) and egg laying (1939) in this 
species. 
These studies were conducted at the Hopkins 
Marine Station of Stanford University, Pacific 
Grove, California, where the author was study- 
ing marine biology as a National Science Foun- 
dation science-faculty fellow. I wish to express 
my appreciation to Dr. L. R. Blinks, director 
of the Hopkins Marine Station, for providing 
facilities, and to Dr. Donald P. Abbott for in- 
troducing me to P. carmelensis. 
REACTIONS TO SALINITY 
Animals were collected from the tide pools 
during low tide at Point Pinos and Carmel 
Point. They were returned to the laboratory and 
placed in a flat, rectangular glass dish through 
which sea water (s.w.) flowed. Solutions of 25, 
50, 75, 100, 125, and 150 per cent s.w. were 
made. The dilute solutions were made by mix- 
ing sea water from the laboratory pipes with 
the appropriate amount of distilled water. The 
concentrated solutions were made by evaporat- 
ing sea water to form a 200 per cent solution 
1 Assistant Professor of Zoology, University of Kan- 
sas, Lawrence. Manuscript received February 25, I960. 
and then diluting this with appropriate amounts 
of distilled water. 
The first experiment was to determine the 
range of tolerance to salinity. Twenty animals 
were placed in each of the dilutions of s.w. They 
were observed for activity every hour during the 
first 12 hr. and then were checked every 12 hr. 
for 5 days. Any animals surviving after 5 days 
were periodically checked for another 2 weeks 
after which time the experiments were discon- 
tinued. Two tests were made for activity. The 
dishes were shaken gently; healthy animals re- 
acted to this agitation by showing some move- 
ment in place or by locomotion. A bright light 
caused normal animals to locomote. Animals 
that did not respond to either stimulus were 
considered inactive until disintegration of epi- 
dermal cells was evident, at which time the 
animals were considered dead. 
23 per cent s.w. All animals curled into a 
U-shaped position immediately upon being 
placed in the dish. After 1 hr. all animals were 
dead. The individuals showed a marked swell- 
ing and disintegration of the epidermal cells. 
30 per cent s.w. Most animals curled into the 
U-shaped position within 10 min. After 1 hr., 
only abnormal body movements, characterized 
by twisting and contractions, were evident. The 
worms would not attach to the dish, and several 
extruded material, including copepods that had 
been engulfed, from the mouth. After 5 hr. 10 
animals were transferred to normal sea water. 
Two hr. later half the worms were active. After 
3 hr., 7 of them were active and the other 3 
were uncurled. By the end of 16 hr. all animals 
displayed normal activity. Seven of this group 
were active 2 weeks later when the experiment 
ceased. 
At 54 hr. 5 of the remaining 10 worms in 
50 per cent s.w. were disintegrating and the 
other 5 showed some slight muscular movement 
when stimulated. The 5 active worms were trans- 
ferred to normal s.w., but none of them sur- 
vived. 
203 
