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Class Turbellaria
Characteristics: Free-living, ciliated epidermis containing rod-like rhabdites (forms a protective mucous
coat), ventral mouth opening, monoecious, both sexual and asexual fission common. Example: planaria
Based on your reading of the text and other background information, formulate a hypothesis regarding
geotaxis and phototaxis of planaria. Before formulating your hypothesis, answer the following questions.
1. Do you think planaria will display a positive or negative geotaxis? Why? ______________________
_____________________________________________________________________________________
2. What is the single independent variable that you will test in this experiment? ____________________
3. What dependent variable will you be monitoring in this experiment? ___________________________
4. In the space below write your hypothesis in an if/then format. Remember, if IV, then DV.
If __________________________________________________________________________________,
then ________________________________________________________________________________.
5. Do you think planaria will display a positive or negative phototaxis? Why? _____________________
_____________________________________________________________________________________
6. In the space below, write your hypothesis in an if/then format.
If __________________________________________________________________________________,
then ________________________________________________________________________________.
Procedure
Part One, Geotaxis
1. Obtain a test tube filled with spring water. Ask your teacher to place a planarian in the test tube.
2. Insert a stopper into the mouth of the test tube. Be sure to insert the stopper firmly so that the test tube
will not leak later when it is inverted.
3. Holding the test tube upright, observe the activity of your planarian. Record your observations for
your lab group number in Table 1.
4. Slowly invert the test tube and observe the planarian’s reaction. Record your observations for your
lab group number in Table 1.
5. Record your data in the class data table on your teacher’s laptop.
6. Once all class data has been recorded, copy the data into Table 1.
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Table 1
Lab Group Number
1
2
3
4
5
6
7
8
9
10
11
12
Observations in upright tube
Observations in an inverted tube
Part Two, Phototaxis
7. Obtain an 8 cm length of Tygon tubing that has been cut in half length-wise. This piece of tubing will
serve as a test trough in which your planarian will swim.
8. Using a disposable pipet, transfer enough culture water to the central area of the piece of split tubing
to make a 4 cm long water puddle.
9. Cover half of the water puddle with foil to create a dark environment. Do not allow the foil to touch
the water.
10. Transfer one planarian into the center of the water puddle of the trough.
11. Observe the planarian’s activities for two minutes. Every ten seconds during this two minute period
note the location of the planarian by placing an X in Table 2 under the appropriate light or dark
column.
Table 2
Time Elapsed
(secs)
0
10
20
30
40
50
60
70
80
90
100
110
120
Dark
Light
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12. Examine a planarian in a distilled water-filled culture dish. Use a stereoscope to aid in your
observations.
13. Draw a picture of the planarian. Label the anterior end, the auricles, the ocelli, the pharynx, the
mouth, the epidermis, and the posterior end.
14. Observe the movements of the planarian. Describe what you see. ___________________________
___________________________________________________________________________________
15. Place a small amount of hard boiled egg yolk into the culture dish with your planaira. Observe the
planaria’s response to the egg. This may take several minutes. Be patient! Write down your
observations.______________________________________________________________________
Analysis and Conclusions for Turbellaria
16. Do planaria exhibit positive or negative geotaxis? Explain your answer using the class data.
17. Do planaria exhibit positive or negative phototaxis? Explain your answer using the data you
collected.
18. What type of taxis did the planarian exhibit in the presence of egg yolk? Explain your answer using
the data you collected.
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19. Planaria exhibit cephalization. What is cephalization?
20. What structure do animals with bilateral symmetry possess that is lacking in asymmetrical and
radially symmetrical animals, and why is it would it be beneficial for most actively crawling or
swimming animals?
21. What embryonic germ layer is present in Platyhelminthes but was absent in the Cnidaria?
22. What kinds of tissues develop from that third germ layer?
23. Turbellarians are monoecious. What does that mean?
Class Monogenea
Characteristics: Monogenetic flukes; mostly ectoparasites on vertebrates; bear opisthaptor; body wall
with tegument. Examples: Gryodactylus and Polystoma
Members of the Monogenea, Trematoda, and Cestoidea possess an outer epidermis modified as a
tegument. It is non-ciliated and is a continuous layer of fused cells. It is adaptive for parasites in these
classes because it aids in the transport of nutrients, gases, and wastes across the body wall and protects the
parasite from being digested by the host’s immune system. Monogenetic flukes have a single generation
in their life cycle, that is, one adult develops from one egg. Most monogenetic flukes are external
parasites of fishes, where they attach to gill filaments and feed on epithelial cells, mucus, or blood.
Unfortunately, examples of this class are not available.
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Class Trematoda
Characteristics: Flukes; body wall with tegument; leaf-like or cylindrical; usually with oral and ventral
suckers; adults are parasites of vertebrates. Examples: Clonorchis and Schistosoma
24. Obtain a prepared slide of a liver fluke (Fasciola hepatica). Using a dissecting microscope, draw a
picture in the space below. Label the oral sucker (located at the anterior tip); it serves as a holdfast
and surrounds the mouth opening. The muscular pharynx is just posterior to the mouth. Just posterior
to the oral sucker locate and label the ventral sucker. The remaining internal structures are
components of the reproductive system.
Class Cestoidea
Characteristics: Tapeworms; body wall with tegument bearing microtriches (increase surface area for
absorption); body consisting of a scolex with hooks and/or suckers and a long tape-like strobila divided
into proglottids; no digestive tract; monoecious; parasites of vertebrates. Examples: Taenia,
Hymenolepis
25. Obtain a prepared slide of a dog tapeworm (Taenia pisiformis). These slides have representative
regions of the tapeworm mounted under one cover slip. Using a compound microscope, locate and
examine the scolex under low power. This is the anterior most part of the tapeworm and is on the far
left of the slide. Label the suckers, the hooks, and the anterior end.
Tapeworm scolex
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26. Just behind the scolex note a number of immature proglottids (2nd from left on the slide). Mature
proglottids (on the far right) are indicated by the presence of reproductive structures and some
fertilized eggs. Gravid proglottids are full of fertilized eggs. In the boxes below, draw both types of
proglottids.
Immature proglottid
Mature proglottid
27. What happens to the size of the proglottids moving from the anterior end to the posterior end?
28. Why is it often necessary for tapeworms to be monoecious?
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Summary
1. What are three major sets of organs that characterize members of the phylum Playthelminthes?
_______________________, _______________________, _______________________
2. The cladogram below illustrates evolutionary relationships among the Platyhelminthes. Fill in the
missing CLASS names.
3. Name at least one derived character for each of the following flatworm classes:
a. Monogenea
____________________________________
b. Trematoda
____________________________________
c. Cestoidea
____________________________________
4. According to the cladogram, which of the four classes of Plathyhelminthes is most closely related to
ancestral members of this phylum? ___________________________________________
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