Download Earthworm Dissection External Anatomy Internal Anatomy

Name _______________________________________
Period ______________
Earthworm Dissection
Directions: Follow the instructions carefully, check the boxes as you complete each
step. Remember that dissection is about carefully exposing the organs to view, try not to
damage structures.
External Anatomy
1. Examine your earthworm and determine the dorsal and ventral sides. The ventral
side appears flatter than the other side of the worm. The dorsal side is the worm’s
rounded top.
Prostomium
2. Locate the clitellum which is on the anterior end of the worm. It is the
swelling located from segments 33 to 37 and is near the anterior end.
3. Locate the prostomium, it is a fleshy lobe covering the mouth of the
worm. It is on the far anterior end of the worm.
4. Locate the dark line that runs down the dorsal side of the worm, this is
the dorsal blood vessel. The ventral blood vessel can be seen on the
underside of the worm, though it is usually not as dark.
5. Label the view and structures A & B in the picture to the right.
Clitellum
Internal Anatomy
B
1. Place the specimen in the dissecting pan DORSAL side up.
Ventral
View __________
2. Locate the clitellum and insert the tip of the scissors about 3 cm behind
the clitellum.
3. Cut carefully all the way up to the head. Try to keep the scissors pointed up, and
only cut through the skin. Be careful not to damage the internal organs.
4. Spread the skin of the worm out, use a dissecting needle to gently tear the septa
(little thread like structures that hold the skin to organs below it)
5. Place pins in the skin to hold it apart, angle the pins out so that they are not in your
way of making observations.
Name _______________________________________
Period ______________
Reproductive System
The first structures you probably see are the seminal vesicles. They are cream
colored and located toward the anterior of the worm. These are used for producing
sperm. Use forceps to remove these white structures from over the top of the digestive
system that lies underneath it.
Circulatory system
The dorsal blood vessel (X) appears as a dark brownish-red vessel running along the
intestine. The heart or aortic arches (Y) can be found over the esophagus (just
posterior to the pharynx). Carefully tease away the tissues to expose the arches of the
heart, they run across the worm. How many aortic arches can you count? ______
5
The ventral blood vessel (Z) is opposite the dorsal blood vessel, and cannot be seen
at this time because the digestive system covers it.
Label the diagram (use the letters next to the bold words above)
Y
X
Z
Digestive System
The digestive system starts at the mouth. You will trace the organs all the way to the
anus and identify each on the worm.
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) . The esophagus
leads from the pharynx but you probably won’t be able to see it, since it lies underneath
the heart . You will find two structures close to the clitellum. First in the order is the
crop , followed by the gizzard . Use the dissecting needle to feel the crop and the
gizzard . The gizzard leads to the intestine which is as long as the worm and ends
at the anus .
Name _______________________________________
Period ______________
Use your scissors to cut open the crop and the gizzard. Which one has the harder
exterior? ___________
Gizzard
Which one (crop or gizzard) would you expect to find the contents to be most ground
up? Why?
Gizzard, because it is further along in the digestive system and it has
the specific job to grind food.
Nervous System
Locate the brain at the far anterior region of the worm. It is very tiny and whitish colored.
If you can't find it, it is probably because it was destroyed when you cut the worm. You
CAN locate the ventral nerve cord by removing the intestines and searching for a white
string-like structure that runs the length of the worm and attaches to the brain.
Remove the intestines and locate the ventral nerve cord.
Name _______________________________________
Period ______________
Earthworm Lab Analysis
(Answer True of False; most of the answers can be found in this worksheet)
1. ____ The brain attaches to the ventral nerve cord. T
2. ____ The dorsal side of the worm is lighter than the ventral side. F
3. ____ The clitellum is located toward the anterior end of the worm. T
4. ____ The esophagus lies beneath the pharynx F
5. ____ The ventral nerve cord and the ventral blood vessel are connected.
6. ____ An earthworm has fourteen aortic arches. F
7. ____ Seminal vesicles are part of the worm's digestive system. F
T
8. Label these structures on the image below: pharynx, esophagus, crop, gizzard, aortic
arches, brain, dorsal blood vessel, clitellum, intestine, seminal vesicles.
Intestine
Gizzard
Crop
Dorsal Blood Vessel
Seminal Vesicles
Pharynx
Brain
Esophagus
Aortic Arches
Clitellum
9. In the diagram above, color the digestive structures green, the circulatory structures
red, the reproductive structures blue, and the nervous system structures yellow.
Name _______________________________________
Period ______________
10. What structure in the earthworm has a similar function as the human heart? Explain
your answer.
Aortic Arches, serve as similar function as the human heart because they
move blood throughout the body.
11. Do earthworms have an anterior and a posterior? Explain your answer.
Yes they do have an anterior and a posterior, the majority of the earthworms organs are
concentrated in the anterior end, and the posterior is primarily intestine and blood vessel
12. What characteristics distinguish an annelid from other worms?
Bilateral symmetry, typically reproduce sexually, hermaphroditic, no respiratory organs,
closed circulatory system
13. Does the earthworm have a closed or open circulatory system? Explain your
choice.
This is an example of a closed circulatory system, because the blood is completely contained within
the vessels and aortic arches.
14.
Place in the
correct order
(number)
_7___ Anus
_4___ Crop
_1___ Mouth
_5___ Gizzard
_3__ Esophagus
_6___ Intestine
_2___ Pharynx
Name _______________________________________
Period ______________
Analysis:
Use the comparison chart to summarize the similarities and differences between the blackworm
and the earthworm. Be specific! Use vocabulary used throughout the worm unit.
Differences:
Traits of a Blackworm
1.
Traits of an Earthworm
1.
Aquatic
Terrestrial
2.
2.
Up to 10 cm in length
Up to 25 cm in length
3.
3.
150-250 body segments
About 150 body segments
4.
4.
Chaetae hairs for grip
Setae hairs for gripping soil
Similarities:
1.
Circulatory System
2.
Digestive System
3.
Segmented
4.
Can regenerate
Name _______________________________________
Period ______________