Lab: Earthworm Dissection

PRE-LAB Kingdom______Phylum______Class______

Part I – Terminology

1. There are several terms you should be aware of before beginning your dissection. These words willhelp you orient yourself when you dissect your worm. Write a description for each area in your lab notebook.

▪Anterior - ______

▪Posterior - ______

▪Dorsal - ______

▪Ventral - ______

Part II – External Anatomy

1. The top of the earthworm is the dorsal side. This is the darker side of the worm. Find the dorsal

side of your worm and describe it above.

2. The bottom of the earthworm is the ventral side. This is the lighter side of the worm. Find the ventral side of your earthworm and describe it above. Each segment of a worm has small pairs of bristles called setae which help it move. Run your fingers up and down the ventral side of the worm to feel the bristles.

3. Once you have felt the bristles, place the earthworm in the dissecting tray dorsal side up. Slightly stretch out the earthworm’s body. With dissecting pins, pin the first (mouth) and the last segments of the earthworm(anus) to the dissecting tray. Tag the first pin with a #1 to mark the mouth. Tag the posterior pin with a #2 to mark the anus.

4. Note the swelling of the earthworm near its anterior side. This is the clitellum. Find the clitellum of your worm and tag with a # 3.

5. Sketch your earthworm in your lab notebook and label the following structures

Anterior

Posterior

Clitellum

Mouth

Anus

6. Record the following data in your lab notebook-

a. Number of segments from anterior end to clitellum: ______

b. Length of earthworm: ______cm

Internal Anatomy

7. .Locate the dorsal blood vessel, a dark line that runs from the anterior to the posterior end of the earthworm. Insert the tip of a pair of scissors about 10 segments from the posterior end. Keep the scissors parallel to the dissecting tray, and cut all the way to the anterior end of the worm. Cut away from your body. Keep the cut as shallow as possible. The body wall of the earthworm is very thin, and the internal organs lie just inside. Note: the major internal organs of the earthworm are anterior to the clitellum. Be very careful when cutting in this area.

8. Spread the skin of the worm out, use a teasing needle to gently tear the septa (little thread

like structures that hold the skin to organs below it)

10. Place pins in the skin to hold it apart. Make sure they lay at angle, and not straight up and down, as it is easier to see the organs.

Digestive System

11. The digestive system starts at the mouth. You will trace the organs all the way to the

anus and identify each on the worm.

a. Find the mouth opening, the first part after the mouth is the pharynx, you will see

stringy things attached to either side of the pharynx (pharyngeal muscles).

b. The esophagus leads from the pharynx in segments 6 to 14 but is hard to see since it lies underneath the five aortic arches. The esophagus helps pass the food from the mouth to the crop. It also aids in the removal of excess calcium in the worm’s body. Tag the esophagus with a #4.

c. You will find two round organs close to the clitellum in segments 15-18. First in the order is the crop(segments 15-16). The crop stores food for the worm. Tag the crop with a #5. The crop is followed by the gizzard(segments 17 and 18). Tag the gizzard with a #6.The gizzard grinds food and leads to the intestine.

d. Locate the intestine. The intestine is the longest organ and ends at the anus. Tag the intestine with a #7.Nutrients are absorbed in the intestine. Inside of the intestine there is a long fold called the typhlosole. The typhlosole helps increase surface area to absorb more nutrients. The intestine ends with the anus. Solid wastes are released by the anus.

12. Describe the function of each digestive organ in your lab notebook .Draw this chart in your notebook.

crop
pharynx
mouth
gizzard
esophagus
intestine
anus

13. Use your probe to feel the difference in the hardness of the crop and gizzard. scissors to open the crop and gizzard. Examine the contents of these organs. In your lab notebook compare and contrast the contents of the crop, and the gizzard. Describe the softness or hardness of each.

Circulatory system

14. Trace the earthworm’s closed circulatory system by following the dorsal blood vessel anteriorly along the midline to the 5 aortic arches, located in segments 7 to 11.Tag the aortic arches with #8. In the posterior section of the worm, use a probe to move aside the intestine, Locate the ventral blood vessel. Tag the ventral blood vessel with #9. The 5 aortic arches pump the blood and move nutrients around in the worm’s body. The arches also connect the dorsal and ventral blood vessels.

Reproductive System

15. An earthworm has both male and female reproductive organs and can produce both eggs and sperm. Locate the male reproductive organs. Find the two seminal vesicles in segments 9 to 13.The seminal vesicles are three-lobed, light colored organs along the sides of the esophagus. Tag the seminal vesicles with a # 10. Two small pairs of testes are located in segments 10 and 11. The female reproductive organs include a pair of small, spherical seminal receptacles located in segments 9 and 10, and a pair of ovaries located in the septum between segments 12 and 13. With the exception of seminal vesicles, most of the reproductive organs are small and difficult to see. Label the seminal vesicles and the seminal receptacle on your lab diagram sheet.

Analysis- Label Diagrams handed out to you and place them in your lab notebook.

16. Take a photo of your earthworm. In the picture, I need to see a piece of paper with your names on it. The photograph will be graded. Any pin which cannot be clearly identified is wrong. Be sure you space your pins so that a SINGLE photo will clearly distinguish all of them. Send the photo via email to

14. Clean your work area as directed by your teacher.

a. Place earthworm only into stinky bin. Throw old paper towels away in trash can.

b. Save dissecting pins that are numbered for another class to use. Set aside.

c. Rinse dissecting tools. Put new paper towels on tray. Place clean tools on tray, along with pointers numbered 1-10.

Student Lab Notebook Contents-

Write a description for each area in your lab notebook.

▪Anterior - ______

▪Posterior - ______

▪Dorsal - ______

▪Ventral - ______

Sketch your earthworm in your lab notebook and label the following structures

Anterior

Posterior

Clitellum

Mouth

Anus

6. Record the following data in your lab notebook-

a. Number of segments from anterior end to clitellum: ______

b. Length of earthworm: ______cm

Describe the function of each digestive organ in your lab notebook .Draw this chart in your notebook.

crop
pharynx
mouth
gizzard
esophagus
intestine
anus

In your lab notebook compare and contrast the contents of the crop, and the gizzard. Describe the softness or hardness of each.

Post Lab- Answer the following questions in complete sentences in lab notebook.

1. Trace the parts of the digestive tract through which food passes where it enters the body, and where solid wastes exit.

2. How could you find out whether an earthworm eats soil or not?

3. In which organ (crop or gizzard) did you find the contents to be most ground up and why?

4. Most major organs of the earthworm did not go beyond segment 32. What did you observe in the posterior segments of the worm?

5. How do earthworms get rid of liquid nitrogenous wastes? Be specific. What system is responsible for this? What are the structures involved?

6. The typhlosole is a fold in the intestine. This folds increases surface area for the intestine to ______.

7. In a short paragraph, explain what you learned or found interesting about this dissection.

Student Diagrams SHEET- NAME______Block_____

Label Parts 1- 14

Word Bank- ventral blood vessel, dorsal blood vessel, 5 aortic arches, clitellum, crop, gizzard, pharynx, intestine, anus, seminal receptacle. Seminal vesicles, segments, ventral nerve cord, prostomium

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