Lab #8 – Worms
RED = not available or required this year
Purpose:
1. To compare the external structures of a variety of worms.
2. To dissect and compare structure of 6 worms.
3. To compare the evolution of worms from past organisms studied.
4. To determine the adaptations that earthworms have for burrowing in soil.
Materials:
The following organisms are for observing only:
Platyhelminthes dipylidium (dog tapeworm)
Platyhelminthes Fasciola hepatica (liver fluke)
Platyhelminthes Taenia (dog tapeworm)
Platyhelminthes moniezia (sheep tapeworm)
Platyhelminthes Fasciolopsis buski (liver fluke)
Platyhelminthes planaria (flatworm)
Nemathelminthes ascaris (round worm)
Spuncaloidea phascolosonca (peanut worm)
Annelida Amphitrite (mud worms)
Annelida nereis (sandworm)
Annelida haemopis (leech)
Annelida lumbricus (earth worm)
The following organisms are for dissecting:
Platyhelminthes planaria (flatworm)
Platyhelminthes Fasciola hepatica (liver fluke)
Platyhelminthes moniezia (sheep tapeworm) – work in pairs
Platyhelminthes Taenia saginta (dog tapeworm) – work in pairs
Nemathelminthes ascaris lumbricoides (roundworm) – work individually or in pairs
Annelida haemopis (leech) – work in pairs
Annelida lumbricus (earthworm) - work individually or in pairs
The following are live organisms – take care when handling:
Annelida lumbricus (earthworms)
Dissecting tray
Hand lens
Dissecting microscope
Paper towels
Dissecting probe
Dropper
Dirt or soil
Vinegar
Scalpel
Pins
Scissors
Biohazard bag
Hand-held light
Procedure: Part 1: Observations of External Structures
1. Create a data sheet for part 1.
2. Observe and draw the 12 different types of worms provided. Label the following parts: mouth or
scolex (with hooks and suckers), anus or proglottids, segments (if present), clitellum (if present),
setae (if present).
3. Give an approximate length of each organism. Make sure to note the color of each organism.
Note the thickness and shape of each organism.
Procedure: Part 2: Dissection of Internal Structures: Planaria
1. Create a data sheet for part 2.
2. Use a medicine dropper to transfer a flatworm to a microscope slide. Gently cover the flatworm
with water.
3. Observe the flatworm under the low power of the dissecting microscope. Notice the shape of its
body. What kind of symmetry does it have? What structural features demonstrate this
symmetry? Does the flatworm appear to have a distinct head and tail? How can you tell?
4. Record your observations.
5. With a scalpel, cut the body of the planaria lengthwise. Observe the internal structure under the
dissecting microscope. Record your observations.
1. Cut the bodyalong the transverse plane near the anterior and posterior ends, as well as in the
middle of the body. Observe all three sections under the microscope. Record your observations.
Notice the circular structure in the center of the body. This is the pharynx, the structure that the
flatworm feeds with. Label it. Notice the two cavities to the sides of the pharynx. These are the
branches of the intestine. Please label these. Find the following structures and label them in
your drawing: Cerebral ganglion (brain), Penis bulb (cirrus sac), Nerve cords, Protonephridia
(flame cell), Ovary, Mouth, Oviducts, Pharynx, Yolk glands, Intestine (anterior and posterior),
Testes, Vas deferens, Circular muscle layer, Longitudinal muscle layer, Eyespot (ocelli).
Procedure: Part 3: Dissection of Internal Structures: Liver Fluke
2. Create a data sheet for part 3.
3. Place a liver fluke on your dissecting tray.
4. Observe the fluke under the low power of the dissecting microscope. Notice the shape of its
body. What kind of symmetry does it have? What structural features demonstrate this
symmetry? Does the flatworm appear to have a distinct head and tail? How can you tell?
5. Record your observations.
6. With a scalpel, cut the body of the liver fluke lengthwise. Observe the internal structure under
the dissecting microscope. Record your observations.
7. Cut the body along the transverse plane near the anterior and posterior ends, as well as in the
middle of the body. Observe all three sections under the microscope. Record your observations.
Notice the circular structure in the center of the body. This is the pharynx, the structure that the
flatworm feeds with. Label it. Notice the two cavities to the sides of the pharynx. These are the
branches of the intestine. Please label these. Find the following structures and label them in
your drawing: Oral sucker, Mouth, Pharynx, Esophagus, Intestine, Nerve ganglia, Ventral sucker, Genital pore,
Uterus, Ovary, Yolk glands, Vas deferens, Vas efferens, Testes (anterior and posterior), Excretory duct, bladder,
pore.
Procedure: Part 4: Dissection of Internal Structures: Sheep or Dog Tapeworm
1. Create a data sheet for part 4.
2. Using the picture below, locate all of the internal structures. Observe and record.
3. When cutting the worm, make sure you cut along the midline as well as transversely. Find all of
the following structures and label them on your drawing: Scolex, Hooks, Suckers, Cephalic ganglia,
Anterior nerve ring, Lateral nerve cords, Excretory vessel, Circular muscle, Longitudinal muscle, Vagina, Uterus,
Ovary, Yolk glands, Vas deferens, Testes, Cirrus sac (containing penis), Excretory canal, Nerve cords
Procedure: Part 5: Dissection of Internal Structures: Roundworm
1. Create a data sheet for part 5.
2. After you obtain your Ascaris lumbricoides, fill your dissecting tray with a small amount of water.
Locate the anterior (front) end of your specimen; this is the end with its mouth. You should be able to
see the mouth with three lips surrounding it.
3. Locate the posterior (rear) end. At this end you will find the worm’s anus. For a male, its posterior end
will be curved, for a female it will be straight. (Using this information predict whether your specimen is
male or female.)
Hypothesis: Sex of Roundworm ________________________
4. Pin the anterior and posterior ends of the animal to the bottom of the pan and carefully slit the
body wall longitudinally (lengthwise) using the scissors or scalpel. Begin your incision as close
to the mouth as possible.
5. Open the body cavity by pinning the sides of the wall to expose the internal contents. Be very
careful not to remove or disturb any organs you will need to identify.
6. The intestine will appear as a thin ribbon-like structure that extends from the mouth to the anus.
All other internal structures are related to its reproduction!
IF YOU HAVE A Female:
7. Locate the genital pore (a slit-like opening about one third of the way down from the anterior end and
connected to a short vagina). This is very difficult to find.
8. The vagina divides into two uteri. At the end of each uterine segment, a thin oviduct can be seen,
followed by the thread-like ovaries. Eggs are produced by meiosis within the ovaries and move along
the oviducts to the uterus. Fertilization of the eggs takes place in the uterus.
IF YOU HAVE A Male:
9. The anus serves both an excretory and a reproduction function.
10. At the posterior end of the intestine, you will find a branch. The area below the branch is the cloaca
(which is connected to the anus on the outside). The cloaca serves as a common collecting area for fecal
material from the intestine and sperm from the seminal vesicle (the thick organ connected to the
intestine at the cloaca).
11. The relatively thick tubes associated with the seminal vesicle are the vas deferens.
12. The finest of the threads are the testes. Sperm are produced in the testes and they mature as they move
along the vas deferens to the seminal vesicle. During copulation, the sperm enter the cloaca before being
deposited in the female.
Use the diagrams to determine for sure if yours is male or female.
Conclusion: Sex of the Roundworm ____________________________
Female
Male
Procedure: Part 6: Dissection of Internal Structures: Leech
1. Create a data sheet for part 6.
2. Pin through the tail with needle and then through the head. Make sure to stretch animal out as far
as possible. If it does not stretch easily, do not force it. You can always stretch if farther after you
cut the body wall.
3. Make a dorsal incision. Carefully separate the skin from the body and pin it down.
4. Examine the internal structures under a dissecting scope. Try to locate the structures illustrated
above. This is not easy due to the large amount of mesenchymal tissue and the oblique muscles.
These tissues can be carefully removed to see internal structure. In any case, note the
mesenchymal tissue, oblique muscles, and the lack of a large coelom and segmental septa. How
does this compare to the internal anatomy of Lumbricus and Nereis?
5. Can you locate any setae? In what plane is the body flattened? All leeches have a constant
number of segments (34), but secondary external annulation obscures the true segmentation
which is apparent in the arrangement of the internal structures. How many annuli are there per
segment in Hirudo? One annulus of each segment is marked by a row of sensory papillae. Five
pairs of dorsal papillae in the first five segments are modified into eyes.
6. The more pointed anterior end of the leech bears a small ventral sucker formed from the
prostomium and peristomium.
7. The posterior end bears a large ventral sucker made up of segments 25-34. The single opening
of the vas deferens is located midventrally at the second annulus of segment 10. The penis issues
from this pore. The vagina opens midventrally at the second annulus of segment 11. Like the
oligochaetes, leeches are hermaphroditic and cross copulation is the rule. Nephridiopores open
lateroventrally at the last annulus of each segment from 6 to 22, but are difficult to see. The
clitellum develops seasonally on segments 9-11 which bear abundant secretory cells.
8. The surface arrangement of the musculature in the leech is similar to the other annelids with an
outer circular layer of muscles and an inner longitudinal layer. Leeches, however, also have
dorsoventral muscles which maintain the compressed shape and aid in locomotion. The
coelomic space is reduced by mesenchymal tissue. This tissue consists of fine capillaries of the
coelomic blood sinus system surrounded by globular cells forming a connected system of
sinuses. The sinus system is continuous between segments and septa are reduced or absent. The
gut is provided with branches called caeca, which increase the surface area for digestion. The
reduction of the coelom and lack of a discrete segmental hydrostati skeleton is reflected in the
method of leech locomotion.
9. Write a conclusion comparing this worm to the others observed in this lab.
Procedure: Part 7: Dissection of Internal Structures: Earthworm
1. Create a data sheet for part 7.
2. Place a paper towel in the bottom of a dissection tray, and moisten it with water. Place an
earthworm on the towel. Identify the dorsal side, which is the worm’s rounded top, and the
ventral side, which is its flattened bottom. Turn the worm ventral side up, as shown in the
diagram below.
3. Use a hand lens as you observe all parts of the worm, externally and internally. Find the
anterior end by locating the prostomium, which is a fleshy lobe that extends over the mouth.
The other end of the worm’s body is the posterior end, where the anus is located.
4. Locate the clitellum, which extends from segment 33 to segment 37. Look for the worm’s setae,
which are the minute bristle-like spines located on every segment except the first and last one.
5. Refer again to the diagram of the ventral view of the worm to locate and identify the external
parts of its reproductive system. Find the pair of sperm grooves that extend from the clitellum to
about segment 15, where one pair of male genital pores is located. Look also for one pair of
female genital pores on segment 14. There is another pair of male genital on about segment 26.
Try to find the two pairs of openings of the seminal receptacles on segment 10. Note: These
openings are not easy to see.
6. Turn the worm dorsal side up. Add water to the tray so that the worm remains moist. Using a
scalpel and scissors, make a shallow incision in the dorsal side of the clitellum at segment 33.
CAUTION: Scalpels are very sharp. Report any cuts to your teacher. Using the forceps and
scalpel, spread the incision open, little by little. Separate each septum from the central tube by
using a teasing needle, and pin down each loosened bit of skin. Continue the incision forward to
segment 1.
7. Use the diagram below to locate and identify the five pairs of aortic arches, or hearts. Then find
the dorsal blood vessel. Look for smaller blood vessels that branch from the dorsal blood vessel.
8. Locate the digestive tract, which lies below the dorsal blood vessel. Refer to the diagram above
to locate the pharynx, esophagus, crop, gizzard, and intestine.
9. To find organs of the nervous system, push aside the digestive and circulatory system organs.
Use the diagram below to locate the ventral nerve cord. Trace the nerve cord forward to the
nerve collar, which circles the pharynx. Find one pair of ganglia above the pharynx. The
ganglia above the pharynx serves as the brain of the earthworm.
10. The worm’s excretory organs are tiny nephridia. There are two in each segment. Use the
preceding diagram to locate some nephridia.
11. Use the diagram below to locate and identify a pair of ovaries in segment 13. Look for two pairs
of tiny testes in segments 10 and 11. To find these organs, you will again have to push aside
some parts already dissected.
12. Dispose of your materials according to the directions from your teacher.
13. Clean up your work area and wash your hands before leaving the lab.
Procedure: Part 8: Identifying Adaptations by an Earthworm for Burrowing in Soil
1. Wet a paper towel and place it in the dissecting tray.
2. Place an earthworm on the wet paper towel.
3. Observe the earthworm and record.
4. Use the dissecting probe to help you count the number of segments on the earthworm. Record
the number next to your sketch of the earthworm.
5. Examine the ventral and dorsal surfaces of the earthworm. Record any differences.
6. Lightly rub your fingers along the earthworm’s body. Describe how it feels.
7. Use the hand lens to find the setae. Observe and record their arrangement on each segment.
8. Use the dropper to place a drop of vinegar in front of the earthworm. Record your observations
of what happens.
9. Replace the paper towel with a clean towel before continuing.
10. Shine the hand-held light at the earthworm from either end. Record your observations of what
happens.
11. Observe the earthworm as it moves about the tray. Watch the movement of each segment.
Record your observations.
12. Return the earthworm to its environment (in the terrarium). Observe it as it moves around the
terrarium.
Conclusion:
a. Draw your conclusions.
i. A detailed comparison of the different organisms you observed in the worm lab.
ii. A detailed comparison of worms to past organisms you have observed.
iii. A hypothesis as to how the organisms you have observed evolved into each other
(past and current lab).
b. What went well while dissecting and observing? Why?
c. What didn’t go so well while dissecting and observing? Why?
d. Questions:
1. Why aren’t wax worms and meal worms included in this phylum?
2. Why does an earth worm look the way it does? Why is it colored the way it is? Why
is it shaped the way it is? Why are the structures located where they are? Refer to
specific structures and use the language of the theories of evolution and natural
selection to answer the questions.
3. Why does a tapeworm look the way it does? Why is it colored the way it is? Why is
it shaped the way it is? Why are the structures located where they are? Refer to
specific structures and use the language of the theories of evolution and natural
selection to answer the questions.
4. What are the defense mechanisms found in each of the specimens studied? Why did
they develop they way they did? Frame your answer using the language of natural
selection.
5. Choose two features from the structures listed in the procedure and explain why they
are in a worm of your choice. Frame your answer using the language of natural
selection.
6. Explain why earthworms have segments while round and flat worms do not. You
may need additional resources to answer this question. Frame your answer using the
language of natural selection.
7. Compare the tape worm to other worms you have observed. Include a discussion of
the following questions. What is the scolex? What is its function? What is a
proglottid? What can be said about the digestive and nervous systems of this
organism? What can be said about the reproductive system of this organism?
8. Discuss how the earthworm uses its setae to aid in movement. Discuss the
adaptations the earthworm may have for burrowing in soil (keep in mind light and
chemicals, as well as pushing soil out of the way). How does moving towards or
away from chemicals (vinegar) or light help the earthworm survive?
9. Include a discussion of how an earthworm’s digestive system has adapted to obtain
relatively small amounts of food from large amounts of ingested soil.