Download Biology 11: Dogfish Dissection

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Biology 11: Dogfish Dissection
Introduction: In this lab you will explore and observe the internal and external structures of the dogfish
(Squalus acanthias) anatomy. Dogfish are cartilaginous fish.
Your sharks have been double injected with latex to make identification of internal
structures easier. Red latex indicates arteries and blue veins.
Background: Dogfish are one of the most common types of migratory sharks, travelling in large
schools. Dogfish can reach sexual maturity around 6-12 years old and can live up to 30
years. They eat small fish and marine animals and are eaten by larger fish and marine
mammals. Dogfish have a poisonous spine located on the dorsal fin for protection
against predators.
Materials:
Preserved Dogfish
Dissecting Tray
Dissecting Guide
Safety Glasses
Gloves
Lab Apron
Scalpel
Scissors
Probe
Tweezers
Dissecting Pins
Procedure:
Through this dissection you will dissect and analyze the various body systems that characterize your
dogfish (and sharks in general). You will start out with the external features of your dogfish and work
your way inwards.
Follow the instructions for each system below and use the checklist (at the end of the package) and
dissecting guide to identify each systems’ structures.
At the end of each system call Mr. Fox over to make sure that you have identified everything correctly.
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Part A: Dogfish External Anatomy
1. Place your dogfish on your dissecting tray and identify the structures listed below:
a) Rostrum: Pointed snout.
b) Nostrils: Water is taken into the smaller of these openings, passes by a sensory membrane that detects
chemicals and then expelled out the larger opening.
c) Spiracles: Small openings just behind the eyes. Allow water to pass over the gills even if the mouth is
closed.
d) Mouth: Functions in obtaining food and allowing water to pass over the gills.
e) Gill Slits: Five vertical slits allowing water to exit the gills.
f) Lateral Line: Pale line running from the pectoral fin past the pelvic fin on the side of the shark. Is a
collection of small pores leading to sensitive nerve receptors below the skin that sense motions in the
water.
g) Cloaca: Exit for the digestive tract and entrance for the reproductive system.
h) Clasper: Found only in male sharks, these extensions of the pelvic fin are used to transfer sperm to
female sharks during mating.
i) Dorsal Spines: Located just behind each dorsal fin and contains a toxin to ward off predation.
j) Placoid Scales: Modified teeth that cover the shark’s
skin.
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2. a) Run your hand from head to tail and then tail to head. Do you notice any difference in texture?
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b) What benefit might the configuration of the placoid scales have to the shark’s swimming ability?
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2. Based on the shape and location of each fin, what type of function or movement do you think it might
provide the shark?
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3. How would the spiracles benefit a bottom-dwelling shark or ray?
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4) What adaptations do dogfish have for their lifestyle?
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Part B: Dogfish Internal Anatomy
1. Place your dogfish ventral side up on the dissecting tray. You will need to remove
the spines using scissors before you do so.
2. Use a scalpel (or scissors if the skin is too tough) to create three left to right
incisions: One just posterior to the mouth, one just posterior to the pectoral fins and
the third just anterior to the pelvic fins. Be careful not to cut too deeply or else you
will damage the organs.
3. Use a scalpel or scissors to continue the existing ventral incision up to your
anterior horizontal incision and down to your posterior horizontal incision. Cutting
through the pectoral and pelvic girdles will be tough and likely require the use of
scissors.
4. Either remove the flaps of skin you have created or pin them back using dissection
pins. This should let you view the organs in the shark’s two body cavities:
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pericardial cavity (containing the heart) and pleuroperitoneal cavity (containing the digestive organs).
Digestive Tract
-The digestive
system is responsible
for chemically and
mechanically
breaking down found
into smaller
compounds that can
be released into the
bloodstream and
transported to body cells.
-To better see the digestive system cut from the middle of the lower jaw on a diagonal towards the gills.
Make sure that you are cutting around the heart!
-Identify and pin the following structures involved
in the digestion of food in the mouth and transfer of
these materials to the stomach:
1. Teeth: Derived from the scales that cover the
shark’s body! Adapted to function as cutting
structures and are replaced regularly as they wear
out.
2. Pharynx: Cavity posterior to the spiracles. Gill
slits open onto either side of the posterior portion
of the pharynx. Gill rakers branching off the gill
arches prevent large food particles from entering
the gills from the pharynx.
3. Esophagus: Short connection between the
phanrynx and the stomach. It is very short and
wide in sharks.
4. Stomach: This J-shaped organ is composed of
two portions, the cardiac (portion near the heart)
and limb (portion after the bend in the stomach),
and ends in the pyloric sphincter, a muscular ring
that can be felt.
5. It can be difficult to tell the esophagus and
stomach apart by their external features, but is very easy if you view their internal structures. Create an
incision through the ventral wall of the esophagus and stomach and open both organs. You may need to
remove part of the liver before you do this to get better access to the esophagus and stomach.
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a) What were the stomach contents?
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b) Wash out the contents of the stomach if necessary and examine the lining of the esophagus and
stomach. The esophagus is covered in papillae projections, whereas the stomach is lined with deep folds
called rugae. Based on your observations, which organ is more suited for mechanical digestion? Why?
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6. Duodenum: First section of the small intestine immediately after the stomach. Digestive fluids from
the gallbladder (bile, originally produced by the liver) and pancreas (pancreatic juice) are secreted into it
and they chemically digest food. Locate the liver, gallbladder and pancreas.
7. Spiral Intestine: Second section of the small intestine. Distinguishable by an extensive network of
arteries and veins on its surface.
-Cut open the spiral intestine and observe its interior structure. What do you think is the purpose of the
spiral valve? How do humans accomplish the same thing in our intestines?
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8. Colon: Third section of the small
intestine. It ends in the anus, which
opens into the cloaca.
9. Rectal Gland: Finger-like
structure leading into the colon that
excretes salt in order to regulate it’s
concentration in the blood.
*Get approval from Mr. Fox before
you carry onto the next section!
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Respiratory and Circulatory System
-The respiratory system functions in gas exchange and
the circulatory system in the transportation of
respiratory gases, nutrients, hormones, defensive cells
and wastes throughout the body.
1. The gills should already be exposed from your
previous explorations, but if they are not trim some of
the excess tissue out of the way using your scissors.
2. When water enters through the shark’s mouth or
spiracles it travels into the internal gill slits to the gill
pouches, which contain the gill lamellae and secondary gill
lamellae that are responsible for gas exchange. The water then
exits the shark’s body through the external gill arches.
3. How are the gill lamellae modified for their function?
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4. How are the gills protected from damage from materials that
may be inside the shark’s mouth?
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5. Once oxygenated, blood travels from the gills through arteries
to the rest of the body. Make sure that you see the high degree of
vascular tissue (arteries and veins) surrounding the gills!
6. Now examine the pericardial cavity and the two chambered
heart. It may be necessary to gently remove some tissue or
membrane obscuring the organ.
*More on the next page!
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6. Identify and pin the following heart structures. You may
remove the heart and cut it open to see its different
chambers.
a) Sinus Venosus: A thin walled, -non-muscular sac that
collects deoxygenated blood from the body.
b) Atrium: Collects deoxygenated blood from the sinus
venosus.
c) Ventricle: Main contracting chamber of the heart.
d) Conus Arteriosus: Muscular reservoir that empties after
the ventricle contracts. It adds pressure to the blood to send
it to the gills.
*Get approval from Mr. Fox before you carry onto the next
section!
Urogenital System
-The urogenital system includes both the reproductive and
excretory organs and structures. These systems are studied
together as they share common ducts.
Excretory System
-The excretory system filters wastes from the blood,
producing urine.
-You will need to remove the digestive tract from its anterior end and the digestive tract from its anterior
end (esophagus) and posterior end (colon).
-Identify and pin the following excretory structures:
1. Kidneys: These two organs extract urea from urine and returns it to the blood. This ensures that the
shark’s body fluids have the same amount of solutes as the surrounding seawater. This prevents seawater
from trying to invade the shark’s tissues and cells (which would kill them).
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2. Rectal Gland: Finger-like organ leading into the colon. It secretes excess salt into the colon for
expulsion from the body.
Reproductive System
-The reproductive organs are responsible for the production of egg and sperm and for fertilization.
Male Sharks
-Identify and pin the following structures:
1. Testes: Produce sperm. Oval shaped and located next to the kidneys and on either side of the stomach.
2. Epididymis: Anterior portion of the kidney that receives the sperm from the testes. *Too small to see.
3. Vas Deferens: A highly coiled tube in adult sharks (straight in juveniles) that carries sperm to the
seminal vesicle.
4. Seminal Vesicle: Enlarged section of the Vas Deferens that adds secretions to the sperm.
5. Sperm Sacs: Receives the sperm containing fluid and passes it through the cloaca to exit the body.
6. Claspers: Modified section of the pelvic fin that transfer the sperm into the female cloaca. Sperm
transportation is facilitated by dorsal grooves in the claspers and lubricating fluid secreted by the siphon
sac.
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*Get approval from Mr. Fox before you carry onto the next section!
Female Sharks
-Identify and pin the following structures:
1. Ovaries: Produce the eggs. Found on either side of the kidneys and actually looks quite a bit like the
liver. In immature sharks they are smooth and small. If you shark is mature sharks the ovaries may
contain eggs.
2. Oviducts: Elongated tubes that contain the eggs when they are ready to be fertilized.
3. Shell Gland: Eggs pass through here on their way to the uterus. The gland secretes a thin membrane
around fertilized eggs. *Too small to be seen.
4. Uterus: Enlarged end of the oviduct where eggs develop. As the offspring develop they are attached to
a yolk sac. You will need to cut through the pelvic girdle to see these structures.
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*Get approval from Mr. Fox before you carry onto the next section!
Nervous System: The Brain
1. Remove the skin from the dorsal section of the head (you will need to flip your shark onto its ventral
side to do this).
2. With your scalpel, carefully shave the shark’s cranium down from the rostrum to the back of the gill
slits to expose the brain, olfactory lobes and major brain nerves. Make sure you shave of thin sections so
that you don’t cut into the brain or nerves! *See image below!
3. Now that you’ve exposed the nervous system, you should be able to identify and pin the following:
a) Olfactory Sacs: Two large bulbous nerve sensors that detect chemical changes in the water. Reached
through the nostrils.
b) Olfactory Lobes: Area of the brain that receives and processes nerve signals from the olfactory sacs.
c) Cerebrum: Two hemispheres between the olfactory lobes associated with sight and smell.
d) Optic Lobe: Prominent lobes in the mid-brain that receive nerves from the eyes.
e) Cerebellum: Just posterior from the optic lobes. Control muscular coordination and position.
f) Medulla Oblongata: At the base of the brain. A widening of the spinal cord that controls many spinal
reflexes.
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Analysis Questions
1. Identifying Relationships What shark organ that you observed is most closely related in function to a
human ear? Explain. (3 Marks)
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2. Identifying Relationships What are two evolutionary advantage jaws provide cartilaginous and bony
fish? (2 Marks)
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3. Identifying Relationships Sharks do not possess a swim bladder. How do they regulate their
bouyancy? (2 Marks)
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4. Interpreting Information What adaptations for life in the water did you observe in the shark? Name
three and describe what that adaptation does. (3 Marks)
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5. Drawing Conclusions Describe the differences between a gastrovascular cavity and a complete oneway digestive system. Which type of digestive system do fish have and why is it considered to be an
evolutionary advance? (5 Marks)
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6. Making Predictions Predict how a fish’s behaviour would change if it had an open circulatory system
instead of a closed circulatory system. (2 Marks)
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