EMIGRATION CREEK PROJECT
Westminster College, Salt Lake City, Utah
Planarian. 1999-2000. Encyclopedia Britannica. http://www.britannica.com/seo/p/planarian/
These small, free-living flatworms are found under rocks in the fresh
water of Emigration Creek where it crosses the campus of Westminster
College. They are classified in the phylumPlatyhelminthes and in the
class Turbellaria. We have identified the Emigration Creek species as
Dugesia tigrina, a common NorthAmerican flat worm.
Planarians are generally zoophagous, feeding on small living
invertebrates and decaying organisms found in their ecosystem.
and other small herbivores. These small herbivores, in turn, eat
"biofilm" of rocks. Planarians may play an role as a "detritivore"
organism. Detritivore organisms gain their food energy with the help
of decomposing fungi and bacteria which, with the help of various
invertebrates, start the fragmentation process of materials that fall
into the stream. A major source of energy input for this detritivore
food chain is the leaves of the local riparian trees. The leaves are
partially decomposed by bacteria and fungi which can then be eaten
by Dugesia and other aquatic organisms.
The planarian eats by using its long, highly muscular pharynx. This
protrudes through the mouth in the presence of food. The tip is placed
against the food and soft or disintegrating particles of tissue are sucked
up into the main gastrovascular cavity by the muscles in the pharynx.
The cavity will be come full of fluid and small bits of tissue after about
30-80 mins of feeding. Individual particles are ingested by pseudopodial
action of large gastrodermal cells.
Planarians are usually between 3 to 15 mm. The colors seen in the North
American genus, Dugesia, are white, grey, brown, and black. The
triangular head contains two eye spots and sometimes tentacles for
gripping. The mouth, or feeding structure called a pharynx, is located on
These soft bodied, ciliated
flat worms move much like
slugs in an undulating
motion. The movie to the
right shows a Dugesia
tigrina from Emigration
Creek moving under a
Dugesia tigrina reproduces both sexually and asexually. Under the appropriate
conditions of temperature and food, asexual individuals pinch in around
mid-length of the worm's body. The pinching continues until the two halves
are complete. Each half will then form a whole worm. This aexual reproduction
occurs only above
10degrees C with the frequency of division increasing to a maximum at 25 to 28
degrees C. Sex organs may develop during the winter and early spring in some
strains of D. tigrina. Planarians are hermaphroditic in that organs for both sexes
develop on each worm. Egg capsules, or cocoons that are oval in
shape and about 5 mm long, are deposited in May and June. As the
water temperature rises the reproductive organs degenerate and in July,
August, and September reproduction may be entirely by fission. By late
autum the sex organs begin to develop again. Fully developed young
emerge and develop without metamorphosis. Planarians are also capable
of reproducing body parts if they have been damagedor removed. This
has made them very popular in laboratory experiments.
1. McCafferty, Patrick W. 1981. Aquatic Entomology. (p.74). Arthur C.
2. Pennak, Robert W. 1978. Fresh-water Invertebrates of the United
States: Second Edition. (p. 116-131). John Wiley & Sons, Inc., USA.
3. Planarian. 1999-2000. Encyclopedia Britannica.
4. Planarian. 2000. The Columbia Electronic Encyclopedia.