Invertebrates & The Fetal Pig
Name:_____________________________Period:___
Dissection Partners’ Names:
______________________________________________
General Overview: We will spend the rest of the semester on our animal dissections. First, you will dissect the earthworm and
crayfish to allow you to examine two invertebrate species. Then, your lab group of 4 students will spend 4-5 days identifying parts of
the fetal pig and participating in a comparative vertebrate dissection where your group will be the “expert” on one type of vertebrate,
but you’ll also have to learn the other vertebrates from the other groups. You will also be individually completing this lab packet
which includes diagrams and questions. Finally, you will have your lab practical exam on your final exam day. This practical will
count as your Performance Exam for this semester.
Grading: The pig dissection is worth 3 grades:
*80 total points for 8 days of dissection participation (10 pts per day). This grade will typically be assigned to the entire
group, but some students may receive different grades because of amount of participation. Your group can earn up to 10
bonus points for exceptional participation.
*100 total points for completion of your individual lab packet (10 pts per page).
*5% of your average for the lab practical test.
Suggested Timeline:
Thur 5/6- Earthworm Dissection
Friday 5/7- Crayfish Dissection
Wed 5/12- Work on Dissection Packet – maybe start external structures
Thursday 5/13- External structures, Anatomical planes and directions, sexing the pig, skinning the pig
Friday 5/20- Muscles, nervous, respiratory, digestive, circulatory
Monday 5/17- Urogenital/ excretory
Tuesday 5/18- Complete packet & review
Wednesday 5/19 – Performance Final & packet due
Participation:
 EACH member of the lab group is responsible for learning all of the parts. At least 2 people in each group must be actively
involved in dissection, but everyone must participate in locating the parts.
 EACH person is required to put in an equal amount of work. You will be graded on your amount of participation.
 EACH person is required to complete an individual lab packet.
 You are expected to be appropriate and a cooperative team member. Additionally, you are expected to treat your specimens,
materials, classmates, teacher, and work station with respect.
Working Ahead: I strongly suggest that you work ahead since the periods always seem to get shorter as the practical gets closer.
However, please work in order and leave time for review! Listen carefully for options for open lab before or after school.
Daily Cleaning: Clean (with soapy water) and dry dissection tools and tray; Bag and box specimens; Colored Pencils, Dissection
Notebook, Pig Mat, and Soaps where they belong; All trash thrown away (in the garbage can); Sink clean; Tables sprayed and wiped
down; Aprons and goggles returned
□ You will lose individual points if you do not help your lab group clean!
□ You may not leave the classroom until you are checked off!
□ If your table is left unclean and not checked off after class ends, everyone will lose points!
EARTHWORM ANATOMY
Earthworms (Lumbricus terrestris) are representative animals of phylum Annelida and class Oligochaeta. Examining external and
internal structures of an earthworm will reveal some major annelid characteristics. Lumbricus is an excellent animal for study because
of its body organization. An earthworm is a segmented animal. Its body plan consists of many rings (annelus means “ring” in Latin).
Each segment, or ring, of an earthworm is numbered in sequence from anterior to posterior end. Organs can be located by finding the
particular segments they are known to be in. An earthworm “map” lists the location of each organ or structure by segment number
(see the laminated handout).
Materials –
Preserved earthworm
Dissecting probe
straight pins
colored pencils
razor blade
hand lens
dissecting pan
Procedures –
1) Identify the anterior (head), posterior (tail), dorsal (top), and
ventral (bottom) sides of a preserved earthworm.
A bandlike structure, the clitellum, separates the body into
two unequal lengths. The shorter section (about 1/3 of the total length)
is the anterior portion. The longer section is the posterior portion.
The dorsal surface is darker than the ventral surface and rounded
toward the anterior end. The ventral surface is flat.
2) Stretch your animal out with the dorsal side up in a dissecting pan.
3) Pin the earthworm to the pan with straight pins. Use one pin at each
end of the worm (figure 1).
4) Starting at the posterior end use the razor blade to cut along the
dorsal surface. Caution: Blade is sharp. Cut away from your fingers.
Take care to cut only through the skin and muscle of your worm.
NOTE: An earthworm’s skin and muscle are extremely thin. A very
shallow cut is all that is needed. Do NOT cut the entire length of worm at one time.
Instead cut 2 – 4 cm sections at a time.
5) Spread the edges apart by carefully cutting through thin membranes
(septa) on the inside of the worm. These septa are continuous with
each groove on the worm’s outside surface.
6) Pin the skin and muscle to the dissection pan as you spread these
tissues apart. Slant the pins out at an angle (Figure 2).
7) Continue to carefully cut and pin your animal until you reach the
anterior end.
8) After you have completely opened your earthworm, identify the
internal organs by using the earthworm “map” and the following
explanations. The organs of each system are listed on the “map” beside
the number of the segment in which they are located. If an organ is in
more than one segment, the segments that it is in are included in
brackets.
Digestive System
The digestive system begins with the mouth and is
followed by the pharynx, on which many strands of muscle
fibers may be observed. The esophagus is a thin-walled
tube which continues posteriorly from the pharynx to
segment 13 or 14. The crop and the gizzard are in segments
14 through 20. The walls of the gizzard are muscular for
grinding food. The walls of the crop are thin. The rest of
the digestive system is composed of the intestine which
continues from segment 20 to the anus, the most posterior part.
 in the diagram to the right – label the parts of the
earthworm’s digestive system
 in figure 3 color all the parts of the digestive system green
Circulatory System
The large dorsal blood vessel carries blood from the
posterior end of the earthworm to the anterior end. Five aortic
arches connect the dorsal and ventral blood vessels. These arches
are sometimes called “hearts” because they help pump blood.
The “hearts” encircle the esophagus.
* in the diagram to the left – label the parts of the earthworm’s
circulatory system
* in figure 3 color all the parts of the circulatory system red
ovary
Reproductive System
The reproductive system consists of seminal vesicles,
seminal Receptacles, ovaries and testes, and the clitellum. The seminal vesicles are three pairs of saclike structures along the
esophagus. Two very small almost dotlike structures, on each side near the seminal vesicles, are the seminal receptacles.
Ovaries and testes are present in your worm but difficult to observe. They are shown in Figure 3 with dotted lines. The
clitellum produces a mucus slime tube during mating.
The reproductive system also includes two sets of pores
visible on the exterior of the worm. Segment 14 has a pair of female
pores and segment 15 has a pair of male pores.
 in the diagram to the right – label the parts of the
earthworm’s reproductive system.
 In figure 3 color all the parts of the reproductive system
yellow
testes
nerves
Nervous System
Nervous System
ganglion
A “brain” (ganglion mass) is a small mass of white
tissue in segment 3. It may be destroyed when dissecting a
worm. The ventral nerve cord is seen as a white “thread”
extending along the worm’s ventral surface from segment 3 to
the last segment.
Because of its ventral location, the nerve cord cannot be seen
well except where organs have been removed.
* In the diagram to the left – label the parts of the earthworm’s
nervous system.
* In figure 3 color all the parts of the nervous system blue
Excretory System
The excretory system consists of paired organs called nephridia. These are
small organs against the lateral (side) walls of the worm. You may need
a hand lens to see them. They are present in almost every segment.


In the diagram to the right – label the parts of the
earthworm’s excretory system.
In figure 3 color all the parts of the excretory system
orange
excretory pore
tubule
Analysis Questions
1) The skin is the organ of respiration in the earthworm. In order for gas exchange to occur there must be some form
of a liquid for the gases to dissolve in.
a)Explain how respiration takes place through the skin of an earthworm.
b) What happens to the earthworm if its skin dries out?
c) What happens to the earthworm, after a heavy rain, when the soil is flooded?
2) a) To which phylum does the earthworm belong? ________________________
b) What is the meaning of this phylum name? ___________________________
3) a) What is the scientific name for an earthworm? _________________________________________
b) To what genus do earthworms belong? __________________________
c) To what species do earthworms belong? _________________________
CRAYFISH DISSECTION
Part A: Introduction
Crayfish are in Phylum _______________ and Class ___________. They have visible exoskeletons made
of _____________. The crayfish have ____ pairs of __________ appendages that are highly modified for
specific functions. In this lab you will locate the external structures of the crayfish.
Part B: External & Internal Anatomy
Label the external anatomy diagram using these choices: cephalothorax, abdomen, telson, carapace,
compound eye, antennae, uropods, antennules, swimmerets, walking legs, cheliped. Also indicate the
anterior, posterior, dorsal, and ventral sides.
rostrum
Cephalic groove
Label the internal anatomy diagram using these choices: brain, green gland, intestine, mouth, gills,
duct from testis/ oviduct, anus, esophagus, digestive gland, testis/ ovary, stomach, heart. Also indicate the
anterior, posterior, dorsal, and ventral sides.
ganglion
Part C: Appendages
1. Write the function of each appendage on the chart below.
2. Find each of the appendages on your crayfish, carefully remove them with scissors and tape them down to a
piece of paper. The appendages should be taped in the order that they appear on the crayfish. Label each
of the appendages on the paper.
Body Section
Appendage
Function
Cephalothorax
Antennules (1 pair)
Antennae (1 pair)
Eyes (1 pair)
Mandibles (1 pair)
Maxillae (2 pairs)
Maxillipeds (3 pairs)
Chelipeds (1 pair)
Walking legs (4 pairs)
Abdomen
Swimmerets (5 pairs)
Uropods (2 pairs)
Telson (1)
Part D: Analysis
1. Name 3 other Crustaceans that closely resemble the crayfish.
2. Which pair of appendages are used to obtain and eat food?
3. Which pairs of appendages are used for swimming?
4. The exoskeleton of the crayfish does NOT grow with the organism. When they outgrow their exoskeleton
they undergo a process called ____________________.
5. Fill in the blanks with the correct answers. Crayfish seize their food with their ____________. The
____________ and ___________ crush and chew the food. The ____________ are the excretory organs.
The ____________ are used for respiration. The brain consists of a pair of ______________. Two large
nerves extend from the ___________, around the esophagus and join the _____________ nerve cord.
FETAL PIG DISSECTION- External Anatomy
1.
2.
3.
4.
5.
6.
7.
Receive your pig.
Rinse it under water (no soap!) and dry.
Label your bag with group members’ names.
Label the diagrams and learn the parts on your pig.
At the given time, put your pig in the bag and place your bag in the assigned box.
Clean your supplies and area thoroughly.
Answer the questions.
Label anterior, posterior,
dorsal, and ventral on the
diagram to the left.
SEXING THE PIG
Female: Females are identified by the urogenital papilla. This is a small, fleshy, cone-shaped
projection ventral to the anus. Locate the female's external genital opening at the base of the
urogenital papilla. The term urogenital indicates that this is the external opening for both urinary wastes
and reproductive cells.
Male: The male's testes (singular=testis) lie in the scrotum, a pouch ventral to the tail. In older
specimens, this area is enlarged and readily visible. In younger animals, a loose pouch may be visible
but the testes may still be in the abdominal cavity, having not yet descended.
Is your pig male or female? _________________ List at least 2 reasons you
know:_________________
_________________________________________________________________________________
Be able to identify both sexes!
FEMALE
MALE
EXTERNAL ANATOMY
Draw lines and label OR
color code on the diagram to
the right.
Abdomen
Ankle
Anus
Elbow
Eye
Foot
Forelegs
Head
Hind legs
Knee
Nares
Neck
Pinna
Shoulder
Snout
Tail
Teats/ Mammary papillae
Thorax
Tongue
Trunk
Umbilical cord
Analysis Questions
1. Complete the classification of the pig:
Domain ______________ Kingdom ________________ Phylum ________________
Class________________ Order __________________ Family _________________
Genus _______________ Species _________________
2. Fetal pigs are placental mammals. This means that the baby develops inside its mother, where it is
connected to her by the placenta, a large organ filled with blood vessels. These blood vessels help
exchange nutrients, gases, and wastes between the baby and mother. Knowing this, name at least 3
other animals that would be considered placental mammals.
3. Using the graph that has been provided, what is the approximate age of your pig?
4. What are the nares and pinnae more commonly called?
5. What is the difference between the thorax and trunk?
6. Define the terms proximal and distal and give an example using both.
FETAL PIG DISSECTION - Skinning the Pig, Muscles, and Nervous
1. After listening to instructions, carefully skin your pig.
2. Learn the muscles using the diagram provided.
3. Learn the major parts of the sheep brain using the diagrams provided. We won’t be finding these
structures on the fetal pig since they are so small!
4. Review!
5. Clean your supplies and area thoroughly.
6. Answer the questions.
HOW TO SKIN THE PIG (BE CAREFUL!)
1.
2.
3.
4.
5.
6.
7.
8.
Place the pig on its back.
Cut a small slit above the umbilical cord (not deep at all!).
Use the probe or your finger to begin to separate the skin away from the muscles underneath. If you
are seeing organs you are going way too deep!
Cut up to the throat and up one cheek.
Cut down one of the forelegs to the paw. Cut around the paw to leave a glove on the pig.
Continue cutting down to the umbilical cord. Cut around the cord (DO NOT cut the cord off) and
continue cutting down to the tail area. Continue separating the skin away.
Cut down one leg to the paw. Cut around the paw to leave a boot on the pig.
You will only skin one half of the pig. That means from the middle of the stomach to the middle of
the back, including one leg, one arm, and one cheek.
MUSCLES
Draw lines and label OR color code the muscles above with the following terms:
Biceps brachii
External oblique
Flexors/ extensors
Gastrocnemius
Gluteus medius/ maximus
Internal oblique
Latissimus dorsi
Masseter
Pectoralis major
Sternohyoid
Trapezius
Triceps brachii
NERVOUS SYSTEM
Draw lines and label OR color code the dorsal
picture of the brain using these terms:
Cerebellum
Cerebrum
Gyrus ( bump on the surface of the cerebrum)
Media/longitudinal fissure
Spinal cord
Sulcus (groove between the gyri)
Draw lines and label OR color code the sagittal
view of the brain using the following terms:
Arbor vitae of cerebellum
Corpus callosum
Medulla
Pons
Spinal cord
Thalamus
Analysis Questions:
1. What do you think the function of the masseter is?
2. What is another name for the tendon of gastrocnemius?
3. What are the 3 types of muscle tissue? For each, tell whether they are involuntary or voluntary and
where they might be found.
4. For every muscle you learned today, what is the muscle type?
5. Describe the differences in how the gyri and sulci look.
FETAL PIG DISSECTION - Respiratory, Digestive, Circulatory, Urogenital
1. After listening to instructions, carefully cut your pig open.
2. Learn the respiratory, digestive, circulatory, and urogenital systems using the diagrams provided.
You are responsible for BOTH male and female urogenital systems.
3. Review! Your test is Friday!
4. Clean your supplies and area thoroughly.
5. Answer the questions.
Label the diagram of the
respiratory system using
these terms:
Larynx
Left lung
Right lung
Trachea
Remember it’s the pig’s left
and right!
DIGESTIVE
On the diagram of the
mouth to the left, draw lines
and label OR color code the
following:
Epiglottis
Hard palate
Soft palate
Tongue
Tooth
CIRCULATORY
Draw lines and label the
diagram of the heart using
these terms:
Left atrium
Left ventricle
Right atrium
Right ventricle
Aorta/ aortic arch
GENERAL INTERNAL ANATOMY
On the diagram to the right, label the
internal anatomy of the fetal pig OR
color code using the following terms:
Urinary bladder
Urethra
Urogenital opening
Diaphragm
Epiglottis
Esophagus
Gall bladder
Heart
Large intestine
Larynx
Liver
Lung
Mesentery (net-like tissue over the intestines)
Pancreas
Pericardium (sac around the heart)
Rectum
Small intestine
Spleen
Stomach
Trachea
FEMALE UROGENITAL
Draw lines and label OR
color code the diagram of
the female urogenital
system using these terms:
Kidney
Ovary
Oviduct
Renal artery
Ureter
Urethra
Urinary bladder
Urogenital opening
Urogenital sinus
Uterus (uterine body)
MALE UROGENITAL
Draw lines and label OR
color code the diagram of
the male urogenital system
using these terms:
Epididymis
Kidney
Penis
Renal artery
Scrotum
Testis
Ureter
Urinary Bladder
Vas deferens
Analysis Questions:
1. Why is the diaphragm important?
2. The rings you see on the trachea are actually made of cartilage. What do you think their function is?
3. What is the function of the ureter and the urinary bladder?
4. Compare the appearance of the hard vs. soft palate.
5. What is the function of the
a. Epiglottis
b. Spleen
c. Liver
d. Mesentery
6. What type of muscle is found in the esophagus?
COMPARATIVE ANATOMY OF VERTEBRATES DISSECTION
A. Locate each of the major structures indicated below. After you do, place a check mark in the blank. Use the “expert” group to help you learn the parts.
Organism
Heart
Liver
Lung
s
Small/
Large
Intestines
Ureter (s)
& Kidney
Cloaca/
Urinary/
Urogenital
Opening
Tongue
Teeth
Pigeon
Stomach
Trachea
Gonads/
Male vs
Female
(Crop/ gizzard)
Feathers, talons,
beak
Spleen,
pancreas
Rat
Snake
Esophagus
Frog
XXX
XXX
Salamander
XXX
XXX
Shark
XXX
XXX
Perch
XXX
XXX
Lamprey
Additional
Structures
XXX
XXX
XXX
XXX
XXX
XXX
XXX
XXX
XXX
Tympanic
membrane
Gills
XXX
Additionally, please make sure you can differentiate the dorsal, ventral, anterior, and posterior sections of each organism.
Classification Review
Complete the classification for each of the organisms.
Organism
Earthworm
Crayfish
Pig
Pigeon
Snake
Frog
Salamander
Shark
Perch
Lamprey
Rat
Domain
Kingdom
Phylum/ Subphylum
Class
Dorsal, pelvic,
pectoral, caudal
fins
Dorsal, pelvic,
pectoral, caudal,
anal fins
mouth