Oceanography: Spiny Dogfish Shark (Squalusacanthias) Dissection
Part I: External Anatomy
First, use web resources to access an external diagram of a dogfish shark.
Use it as a visual aid to guide you through the checklists below.
Check
Structure
1. External Nares
Function
Pair of openings (nostrils) on each side of the head, cranial from the eyes.
Water is taken into the smaller of the two openings and expelled through
the larger opening. The water passes by a sensory membrane allowing
the shark to detect chemicals in the water.
Small openings caudal from the eyes. These openings allow water to
pass through the gills even when the shark’s mouth is closed.
Although the eating function is evident, the mouth is also used for the
intake of water that passes through the gills.
Five vertical slits which allow water to exit after passing over the gills.
They are located caudally from the mouth. 5. Lateral Line – A pale line
that extends noticeably from the pectoral fin past the pelvic fin. This line
is actually a group of small pores which open into the underlying lateral
line canal, a sensory organ that detects water movements.
Exit from the digestive tract combined with being the opening for the sex
organs. The cloaca lies between the pelvic fins.
Found on male sharks only, these are finger-like extensions of the medial
edge of each pelvic fin. They may have a single spine associated with
each clasper. The claspers aid in sperm transfer during mating.
This is the pointed snout at the cranial end of the head.
Anterior to each dorsal fin is a spine that is used defensively by the shark.
Each spine has a poison gland associated with it.
2. Spiracles
3. Mouth
4. Gill Slits
5. Cloaca
6. Clasper
7. Rostrum
8. Dorsal spines
Additionally, located the following fins:
9. _____Dorsal fin
10. _____ Caudal fin
11. _____ Pelvic fin
12. _____ Pectoral fin
Part I Pre-Lab Questions:
1. How is the shark’s nose different from our own?
2. Why are the Spiracles important?
3. The mouth of the shark is part of which organ system(s)?
4. What is the function of the Gill Slits?
5. What does the Lateral Line do?
6. What two organ systems is the Cloaca a part of?
7. Since the Clasper is only present on male dogfish sharks, what gender is your shark?
8. How many fins does a dogfish shark have?
9. What’s another name for the Rostrum?
10. Where are the Dorsal Spines located?
Part II
Part IIA: Internal Anatomy Dissecting Muscles
Place your shark ventral side down to begin. You will need to flip the shark over after step one to complete this
section.
1. Remove each of the dorsal spines by cutting where it meets the body. This will prevent you from stabbing
yourself unintentionally.
2. Flip your shark over onto its back.
3. Make a mid-ventral incision from the cloaca cranially to just below the jaw. Make your incisions shallow.
4. Cut around the head, around each fin, around the spircles, and around the cloaca.
5. From the cloaca cut dorsally around the shark – this will make a circle around the tail. Remember you are
cutting through the skin only.
6. Using the handles of your scissors or your gloved fingers carefully peel off the skin to expose the muscles.
Before proceeding with additional cuts, check your sharks for the following muscles:
Check
Structure
1. Myotomes
2. Epaxial muscles
3. Adductor
Mandibulae
4. Pectoral Abductor
5. Pectoral Adductor
6. Hypaxial muscles
Function
Segments of muscles in the trunk and tail that are arranged in a unique
zigzag pattern.
Myotomic muscle groups located on the dorsal side.
Large muscles, just caudal from the eye, are the main muscles in closing
the jaw.
Muscle moving away from body wall and connecting to pectoral fin
Muscle moving toward body wall connecting to pectoral fin
Myotomic muscle groups located on the ventral side.
Part IIA Questions:
1. How did you position your shark to remove the Dorsal Spines?
2. How did you position your shark once you remove the Dorsal Spines?
3. In step 2 you made an incision from where to where?
4. Was the shark’s skin as thick as you expected it to be? Why or why not?
Part IIB: Internal Anatomy Dissecting the Abdominal Cavity
1. Place your shark ventral side up on the dissection tray.
2. Make an incision cut from the left side of the jaw ventrally down to just above the cloaca.
3. From the cloaca make transverse (side to side) cuts around the shark.
4. From the pectoral girdle, make transverse cuts around dorsally.
5. You may pin the flaps of muscle tissue to the dorsal sides of the shark or remove the tissue and place to the side
so you can cover the internal organs overnight.
Before proceeding with additional cuts, check your sharks for the following organs:
Check
Structure
1. Esophagus
2. Stomach
3. Duodenum
4. Liver
5. Pancreas
6. Spleen
7. Rectum
Part IIB Questions:
1. Use your textbook and internet resources to describe the function of the following 7 organs:
a. Esophagus
b. Stomach
c. Duodenum
d. Liver
e. Pancreas
f. Spleen
g. Rectum
2. How does the ratio of digestive surface to shark size compare to the digestive surface to body size ratio in
humans?
Part IIC: Internal Anatomy  Dissecting the Circulatory System
1. Lift the flaps over the area of the heart and pin them where they stay out of the way.
2. It may be necessary to cut some tissue that may be attached to the heart.
You should now be able to identify the some of the structures that are listed below.
Part IID: Internal Anatomy Mouth Structures
1. Examine inside the shark’s mouth.
Check your sharks for the following organs:
Check
Structure
1. Atrium
2. Ventricle
3. Teeth
4. Pharynx
5. Gill rakers
Shark Post-Lab Questions:
1.) Make an external sketch of a typical shark. Label the following structures: spiracle, mouth, gill slits, anal
fin, pectoral fin, pelvic fin, dorsal fins, caudal fin.
2.) Describe how skates and rays differ from the typical members of the class chondrichthyes.
3.) Compare and contrast stingrays, electric rays, and skates.
4.) One of the challenges facing fish is buoyancy. How do the members of class chondrichthyes and
osteichthyes deal with this problem differently?
5.) Describe how the following body shapes of fishes are well adapted for the fishes’ lifestyle, and give an
example of a fish with each shape.
a. Streamlined
b. laterally compressed
c. flattened.
6.) What are chromatophores?
7.) What are iridiophores?
8.) Sketch a typical chromatophore.
9.) How do chromatophores and iridiophores assist in camouflage?
10. Differentiate between the two members of class Agnatha discussed in your notes.
11. What characteristics separate fish in class Agnatha from Chondrichthyes and Osteichthyes?
12. Describe the differences between the following type of coloration:
a. Warning
b. Cryptic
c. Disruptive
d. countershading.
13. What are myomeres? How do the following different types of fins aid in locomotion- pectoral, anal, and
pelvic.
14. Describe how feeding adaptations are unique in whale sharks and basking sharks from most other sharks.
15. Discuss how the shapes fish mouths are well-adapted for their feeding habits.
16. All fishes have a two chambered heart. Examine figure 8.15 on page 157. Describe the path blood take in
the circulatory system of a fish.
17. How is this path different than how blood moves through mammals?
18. Why is it useful for skates and rays to have their spiracles on the dorsal surface? *hint: it has to do with
where they live!
19. How do fishes smell?
20. How is this a particularly useful sense for sharks?
21. Some bottom dwelling fish use structures called barbels for taste. What are these structures?
22. What is the lateral line system?
23. What is the ampullae of Lorenzini? What purpose does it serve in sharks? Look at the photo on page 148
and find these structures. What do they look like?