Download Name Date Earthworm Dissection Lab Objectives: Describe the

Name
Date
Earthworm Dissection Lab
Objectives:
 Describe the external anatomy of the earthworm.
 Identify organs that make up the earthworms circulatory system, nervous system,
reproductive system and excretory systems.
 Name and describe the appearance of organs that make up the earthworm’s
digestive system.
Materials:
 Safety equipment: gloves, goggles, lab apron, hair tie, long pants, closed shoes
 Paper Towel
 Water in a small beaker and pipette
 Preserved Earthworm
 Dissection Tray
 Dissection tools: dissecting pins, forceps, scissors, scalpel, teasing needle, probe
 Hand lens
 Plastic storage bag and tie
Background Information:
Among the most familiar invertebrate animals are the earthworms, members of the phylum
Annelida. The word annelida means ringed and refers to a series of rings or segments that
make up the bodies of the members of this phylum. Internally, septa, or dividing walls, are
located between the segments. There may be more than 100 segments in an adult
earthworm.
The earthworm takes in a mixture of soil and organic matter through its mouth, which is
the beginning of the digestive tract. The pharynx draws in the mixture, which is located in
segments 1- 6. Digestive enzymes in saliva are secreted into the pharynx to begin chemical
digestion. The esophagus, in segments 6 – 13 act as a passageway between the pharynx and
the crop. Calcium carbonate is secreted into the esophagus to neutralize the acidic soil
before the material passes into the crop. The crop stores food temporarily before it
passes to the gizzard. The mixture that the earthworm ingests is ground up by muscular
contractions of the gizzard. In the intestine, which extends over two-thirds of the body
length, digestion and absorption take place. Now that the food is in much smaller particles
from the action of the gizzard, it is ready for more chemical digestion from enzymes that
are secreted in the intestine. The food is chemically digested all the way down to the
smallest monomer organic molecules, which are absorbed through the thin walls of
intestine into the blood vessels to be transported to every cell in the body. The
undigested part of the soil passes out of the worm through the anus.
Procedure Checklist: Put a check mark next to each step you have completed!
 Put on safety goggles, gloves, and a lab apron.
 Place a paper towel in the bottom of a dissection tray, and moisten it with water
and place an earthworm on it.
 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.
 TEACHER CHECK 1 ______
 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.
 Locate the clitellum, which extends from segment 33 to segment 37. Look for the
worm’s setae, which are small bristlelike spines located on every segment except
the first and last one.
 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 mail genital pores
is located.
 Look also for one pair of female genital pores 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.)
TEACHER CHECK 2 ______
 Turn the worm dorsal side up.
 Add a little bit of 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
clitellium at segment 33. As you cut, stay just below the layer of skin.
 Use the scissors to cut carefully all the way up to the head. Try to keep the
scissors pointed up, and only cut through the skin.
 Using the forceps and scalpel, spread the incision open, little by little. Use a teasing
needle to gently tear the septa (little thread like structures that hold the skin to
organs below it). Pin down each loosened bit of skin. Place the pins in the skin to
hold it apart from the digestive tract; angle the pins out so that they are not in
your way. Continue cutting and pinning forward toward the anterior end of the worm
to segment 1 (The prostomium).
 Use the diagram below to locate and identify the five pairs of aortic arches, or
hearts on your worm.
 Then, find the dorsal blood vessel. Look for smaller blood vessels that branch from
the dorsal blood vessel.
 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.
 To find the 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. And another pair
of ganglia, masses of tissue containing many nerve cells, above the pharynx.
 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.
TEACHER CHECK 3 ______
 Near the end of the period, Put a paper towel over your earthworm and wet it;
empty your beaker and put it in the tray next to the worm, Dry your tools and wrap
them in a paper towel and put into their holder. Put the tool holder into the
dissecting tray next to the worm; Put the tray in a large plastic bag and tie with a
twisty tie. Label your bag with masking tape and sharpy. Leave your bagged tray at
your station. You will be dismissed by station.
 TEACHER CHECK 4 ______
 When you have completed the lab and when given permission by the teacher, wrap
your earthworm in a paper towel and place it in the plastic bag. Leave this bag at
your table. Rinse out your dissecting tools and your dissecting tray so they are
clean, use a paper towel to dry the tools and tray off so they are dry. Leave your
tools on a paper towel at your lab station. Leave the tray at your lab station.
Clean up your station entirely. You will be dismissed by station.
 TEACHER CHECK 5 ______
Analysis:
1.
2.
Label the diagram with the organs of the circulatory system.
What is the pathway that food passes through the digestive tract? Label the organs
in order.
_________
3. Describe the functions next to the name of each digestive organ and label them on
the drawing.
a. Crop
b. Mouth
c. Pharynx
d. Intestine
e. . Gizzard
f. Anus
g. Esophagus
h. Pharyngeal Muscles
4.
Which parts of the earthworm serve as its brain? How are these parts connected to
the rest of the body?
___
5.
How might you be able to tell using dissection whether an earthworm eats soil?
_________
6.
How would you be able to tell the difference between the crop and gizzard using a
dissecting probe? _____________________________________
7.
Among the earthworm’s structural adaptations are its setae. How do you think the
earthworm’s setae make it well adapted to its habitat?
8. How is the earthworm’s digestive system adapted for extracting relatively small
amounts of food from large amounts of ingested soil?
9.
Your dissection of the earthworm did not go beyond segment 32. What will your
observe if you dissect the remainder of the worm to its posterior end?
10. For the picture below, color the organ systems for the earthworm using the following
key: Circulatory System – Red, Reproductive System –Blue, Digestive System – Green,
Nervous System – Yellow, Skin (outer) – light brown or beige
Use extension lines and label the pharynx, esophagus, crop, gizzard, aortic arches, brain,
dorsal blood vessel
11. On a separate piece of paper draw and label the parts of the earthworm you observed.
Put your name on it and attach it to your lab.