Name ___________________________________________ Date ____________ Period ______
Partner’s Name ____________________________________________________
Annelida
Purpose:
 Describe metamerism and tagmatization and explain why they are important in annelids.
 Describe the annelid body form.
 Recognize class representatives.
 Characterize each of the annelid classes studied including habitat, feeding and
reproductive habits, and distinctive features of body organization.
 Describe the structure and function of organ systems studied in each class.
Materials
Sand worm
Earthworm
Leech
Hand lens
Scalpel
Forceps
Dissecting pan
Gloves
Scissors
Storage bag
Probe
Experimental Procedures:
Class Polychaeta
1. Examine a preserved sand worm. Remember, do not open the jar.
2. Draw a picture of the sand worm. Label the parapodia, the setae (attached to the parapodia)
the tentacles, the segments, and the anterior and posterior ends.
3. What is the function of the parapodia? ___________________________________________
4. What is the Greek translation of Polychaeta? ______________________________________
5. What is the habitat of polychaetes? ______________________________________________
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Class Clitella
This class is named for the presence of the clitellum which is used in cocoon formation. In
leeches, the clitellum is present only in the spring when most leeches breed. Furthermore,
members of this class are monoecious, lack parapodia, and have less setae than polychaeta.
Some leeches have no setae.
Subclass Hirudinea
6. Examine a preserved leech. Remember, do not open the jar. The leeches taper at the anterior
end.
7. Draw a picture of the leech. Label the segments, the anterior sucker, and the posterior
sucker.
Subclass Oligochaeta
8. Obtain a dissecting tray and a set of dissecting instruments. Place an earthworm in the tray.
9. Examine the external features of the earthworm. The slightly swollen area in the anterior
third of the worm is the clitellum. The location of the clitellum will help identify the anterior
end of the earthworm.
10. What is the function of the clitellum? ___________________________________________
11. How many segments are there before the clitellum? Yes, you need to count them. _______
12. Run your finger very lightly along the sides of the earthworm. The bristlelike structures you
feel are called setae. They are slightly curved and have pointed ends. There are four pairs of
setae on each segment. The setae are manipulated by muscles attached at the base of each seta.
13. What is the function of the setae? ______________________________________________
14. The anterior end of the worm has a mouth opening. The lobe over the mouth is the
prostomium. Locate the prostomium.
15. The first TRUE segment, which has the mouth and is just posterior to the prostomium, is the
peristomium. Locate the peristomium.
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16. Locate segment 15. The openings of the sperm ducts are on the ventral surface of a
metamere (segment). Make sure you examine them.
17. Draw a sketch of the earthworm from the side. Label the anterior and posterior ends, dorsal
and ventral surfaces, metamere, clitellum, prostomium, and peristomium.
Internal Anatomy
18. Place the earthworm in a dissecting pan with the dorsal side up. Pin the worm down at the
anterior and posterior ends and down the outside edges. Be careful NOT to stick a pin in the
midline of the worm.
19. Using a sharp scalpel, make a shallow longitudinal cut along the dorsal surface of the worm
from the anterior end towards the posterior end. The incision should stop about 15 segments
posterior to the clitellum. Be sure not to cut into the dorsal blood vessel and the intestinal tract.
20. The body wall is held in place by septa (internal divisions between metameres).
21. Using the scalpel, cut the septa along the length of the worm on both sides of the intestine.
These septa divide the coelom into separate cavities. Pin the body wall to the bottom of the pan,
inclining the pins away from the worm.
22. Begin your observations of the internal structures.
Digestive System
23. Observe the digestive tract running from the mouth to anus. Just posterior to the mouth
opening is the muscular pharynx. When the muscles associated with the pharynx contract, food
particles are sucked into the mouth.
24. The esophagus is posterior to the pharynx and is surrounded by cream colored bodies that
will be studied later.
25. The esophagus expands into a thin-walled storage structure, the crop. Probe the wall of the
crop gently. Note its texture.
26. Just posterior to the crop is the muscular gizzard. This is a grinding structure with thick,
muscular walls. Gently probe it to feel the difference between the gizzard and the crop.
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27. Food is passed from the gizzard to the intestine, where further digestion and absorption
occur. The intestine ends at the anus.
Circulatory System
28. Circulation in the earthworm is through a series of closed vessels. The two main vessels that
can be seen in your dissection are the dorsal and ventral blood vessels.
29. Locate the dorsal blood vessel, the dark line running along the dorsal surface of the digestive
tract, in which blood moves anteriorly.
30. In the ventral vessel, blood usually moves posteriorly.
31. Segmental branches off the ventral vessel supply the intestine and body wall with blood.
32. In metameres 7-11, these segmental branches are expanded into five pairs of “hearts” or
aortic arches. Although these are contractile, they only function in pumping blood between
dorsal and ventral vessels, not throughout the entire body.
33. Locate the aortic arches; they are dark, expanded structures on either side of the esophagus.
Excretory System
34. Highly evolved metanephridia are organs of excretion in the earthworm. Using a hand lens
if necessary, note the coiled tubule attached to the body wall of each segment. These are the
metanephridia.
35. Body fluids, ammonia, and urea are drawn into the tubules and excreted through the
nephridiopores.
Nervous System
36. The nervous system consists of a ventral nerve cord, segmental ganglia, and a pair of large
ganglia anterior and dorsal to the pharynx.
37. In segment three, locate two small white structures. These are known as suprapharyngeal
(cerebral) ganglion or the “brain.”
38. In the region of your worm where the intestine was removed, see if you can locate the
ventral nerve cord.
Reproductive System
39. The testes and ovary are too small to see.
40. In segments 9-12, on either side of the esophagus, locate the white seminal vesicles. These
vesicles store the sperm made in the testes until copulation.
41. In segments 9 and 10, locate two pairs of small, round, cream-colored structures. These are
the seminal receptacles and they receive sperm during copulation.
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42. Clean up by throwing all parts of the earthworm into the trash. No flesh should be put in
the sink. Rinse and dry the dissecting pan. Wipe off all dissecting instruments and dry them
thoroughly.
Teacher’s signature is required after clean up ______________________________
Be sure you can identify the following structures:
_______Crop
_______Dorsal blood vessel
_______Gizzard
_______Aortic arches
_______Intestine
_______Seminal vesicles
Conclusions:
1. What is metamerism, and give two reasons it is advantageous for annelids? (3 points)
2. What is tagmatization? Explain how one annelid examined in this lab exhibits tagmatization
(2 points). Be specific.
3. How does one determine dorsal and ventral surfaces of an earthworm? (1 point)
4. What is the name of the cavity that separates the body wall and intestines? (1 point)
5. What is the function of the pharynx of an earthworm? (1 point)
6. What type of circulatory system do all annelids have? ________________ Why is this
superior to the open circulatory system of the majority of animals we have studied so far? (2
points)
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7. What is the function of the metanephridia? (1 point)
8. How are the seminal vesicles and the seminal receptacles different from one another? (2
points)
9. All annelids share common characteristics. Name two characteristics that polychaetes share
with Clitellata (2 points).
10. What are two reasons that sand worms and earthworms are grouped in different classes? (2
points)
11. Name one reason that leeches and earthworms are in the same class (1 point)
12. What are two ways in which annelids are more complex than mollusks? (2 points)
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