Name______Date______Period ______

Planaria Hysteria!

Background: Planaria, a flatworm, is a common freshwater member of the phylum Platyhelminthes. Planaria are common to many parts of the world and reside in fresh water ponds and rivers. They are also commonly found residing on plants. It moves by beating cilia on the outside, allowing it to glide along on a film of mucus. Some move by undulations of the whole body by the contractions of muscles built into the body wall.

Planarians exhibit an extraordinary ability to regenerate lost body parts. For example, a Planaria split length wise or crosswise will regenerate into 2 separate individuals. The size ranges from 3 to 12mm, and the body has two eye-spots (also known as ocelli) that can detect the intensity of light.

The eye-spots of planarians act as photoreceptors and are used to move away from light sources. Planaria have 3 germ layers (ectoderm, mesoderm, and endoderm), but lack a body cavity or coelom. They have a single- opening digestive tract.

The planarian has very simple organ systems. The digestive system consists of a mouth, pharynx, and an intestine. The mouth is located in the center of the underside of the body. The pharynx connects the mouth to the intestines. The intestines of the Planaria branch throughout the body. They eat living or dead small animals which they suck with their muscular mouth. From there the food passes through the pharynx into the intestines and digesting of the food takes place in the cells lining the intestine, which then diffuses to the rest of the body. The undigested food leaves through the pharynx and mouth.

Planaria receive oxygen and release carbon dioxide by diffusion. The excretory system is made of many tubes with many flame cells and excretory pores on them. Flame cells remove unwanted liquids from the body by passing them through ducts that lead to excretory pores where the waste is released on the dorsal surface of the planarian.

At the head of the planarian there is a brain under the eyespots. From the brain there are two nerve cords which connect at the tail. There are many transverse nerves connected to the nerve cords which make it look like a ladder. With a ladder-like nerve system it is able to respond in a coordinated manner.

A planarian can reproduce either asexually or sexually. In asexual reproduction the planarian detaches its tail end and each half regrows the lost parts. In sexual reproduction each Planaria gives and receives sperm. Planaria have both testes and ovaries. Eggs develop inside the body and are shed in capsules. Weeks later the eggs hatch and grow into adults. Planarians can also reproduce by regeneration. If a Planaria is cut into two halves both halves may become two new Planaria (regeneration).

Purpose: To understand how a Planarian responds to its environment. To observe Planaria regeneration.

Procedure: Take a Planarian out of the culture jar and place it on a slide under the scanning objective of your microscope. Collect Information (use your textbook and background information to answer the following questions):

1. Identify the Kingdom to which flatworms belong?

2. Identify the Phylum to which flatworms belong?

3. What are the basic characteristics of all flatworms?

4. In addition to planaria, what other animals belong to Phylum Platyhelminthes?

5. Describe the type of environment in which you will find most planaria.

6. Outline the process of digestion within a planaria. Do planaria have a complete or incomplete digestive tract?

7. Briefly summarize the nervous system of the flatworm.

8. List the ways through which planaria are able to reproduce.

Observations:

9. Observe your planarian under the dissecting microscope. Sketch your planarian. Label the eyespots, anterior, and posterior end. 10. What type of symmetry is exhibited in the planarian flatworm?

11. Measure the planarian. This operation is best performed by waiting for the worm to stretch out.

Measure the length of the worm in millimeters. Length of planarian: ______mm

12. Observe the planarian for three to five minutes. Record your any and all observations during this time.

Does the planarian seem active or passive? How does it appear to move? Does it swim or “creep”? Where in the dish does it spend most of its time? Etc.

Minute 1 Minute 2 Minute 3 Minute 4 Minute 5

13. How does your planarian react to light? You can perform a simple experiment by turning of your light source and observing the worm’s reactions. Record your observations.

14. Use this diagram to decide which method your group will use to cut the planarian. Circle your choice.

Bisect Lengthwise Two heads Two bottoms Trisect 15. Based on the cut of your choice, generate a hypothesis explaining how you think the planarian will regenerate. You might even want to include a drawing with your hypothesis.

16. To limit the movement of the planarian, you will want to soak up the excess water with a paper towel, being careful not to touch the worm. Cooling the dish with ice may also help to slow down the movement of the planarian. Using a razor or a plastic coverslip, cut the worm according to the diagram your group has agreed upon.

17. Make any initial observations about the head fragment and the size of the tail fragment. Record those observations under “Day Zero” on the table below.

18. After you cut the planarian, how does the mobility of the tail fragment compare with the mobility of the head fragments? If they move differently, explain why you think this is.

19. What environmental factors do you think will affect the regeneration of planaria?

20. Data:

Day Zero Day One Day Two Day Three Day Four Day Five Day Six

Day Seven Day Eight Day Nine Day Ten Day Eleven Day Twelve Day Thirteen