[Oyster Anatomy Laboratory]

Materials:

Aquarium and supplies
  (see Aquarium Set-Up)
Live oysters and paired oyster valves
Dissecting tray or metal pie pan
Oyster knife

 

Sturdy gloves
Stereomicroscope
Large magnifying glass
Dissecting kit
Paper towels

    

Procedure

External anatomy: Observation and Investigation

We will use paired empty shells for this part. As you hold the oyster, be careful - some edges of the shell can be very sharp. Observe the shells or valves (Figure 1).


1. How many valves are there?
1     2     3     4     5     Clear your answer


2. What general name is given to a mollusk with this many valves?
Univalve     Bivalve     Cephalopod     Clear your answer

The oyster is more pointed at one end than the other. This pointed end, the anterior, is called the umbo. It is also the oldest part. The posterior end is the larger, curved end (Figure 2).

On the inside of the valves you will notice an area of pigment where the adductor muscle was located (Figure 3).


3. What is the function of this muscle?
Moving from place to place     Opening and closing     Pump for filtering food     Clear your answer

Hold the oyster valves together so that the flatter one is on top and the umbo points toward you (Figure 4).


4. Are the valves different in size?
Yes     No     Clear your answer


5. If so, which seems larger?
Top valve     Bottom valve     Clear your answer

The flatter of the two valves is the right valve. The cup shaped valve is the left valve (Figure 5).


6. Locate the right valve.


7. Locate the left valve.

The height of the oyster is the distance from the umbo to the edge of the opposite end or bill (Figure 6).


8. Determine the height of your specimen (1 in= 2.54 cm).

Located at the base of the umbo is the hinge (Figure 7). The right valve has a projection that fits into a groove in the left. A ligament joins the two valves at the hinge and assists in opening and closing the valves.


9. What kind of human joints are similar to the oyster hinge?
Knee     Elbow     Shoulder     Hip    
Knee & Elbow    Elbow & Shoulder     Shoulder & Hip    Clear your answer

Now examine the valves for artifacts of other organisms that may have been living on your oyster.


10. Can you find artifacts of these commensal and these parasitic organisms?
  • Barnacle (Balanus spp.)
    Empty barnacle shell on an oyster.

  • Barnacle (scar) (Balanus spp.)
    A "footprint" scar showing the evidence of previous barnacle attachment to an oyster shell.

  • Boring Sponge (Cliona spp.)
    This picture shows the numerous holes produced by this type of sponge.

  • Lacy Crust Bryozoan (Conopeum spp.)
    This picture shows the delicate crust on an oyster shell produced by this colonial animal.
    
  • Hooked Mussel (Ischadium spp.)
    This picture shows the byssal threads remaining after a hooked mussel has been detached from an oyster.

  • Oyster Mud Worm (Polydora spp.)
    This picture shows the burrow that can be seen on the inside of the oyster shell. The dark spot that is formed is called a "blister".

  • Limy Tube Worm (Hydroides spp.)
    This picture shows the calcareous tube remains on an oyster shell.

  • Oyster Spat Scar (Crassostrea spp.)
    This picture shows the smooth scar of the left valve of an oyster spat.

 
Click on the name of each organism to see what the artifact may look like (a new window will open).

Internal Anatomy: Observation and Investigation

If your salivary juices are not flowing by now, then get your creative juices working. For centuries people have been devising ways to get the "meat" out of the oyster. These techniques are referred to as "shucking."


11. Describe or sketch different methods you might use to shuck an oyster.

If you would like to open your own oyster try the method below, otherwise have your teacher shuck the oyster for you.

Hinge Method

Step 1: With your gloved hand, firmly hold the posterior end of the oyster against a hard surface. Make sure that the right valve is facing up. Using an oyster knife with a short blade, insert it into the hinge (Figure 8).

Step 2: Rotate the knife until the pressure pops the hinge (Figure 9).

Step 3: Move the knife around the upper edge of the right valve until the adductor muscle is felt -- sever it. Place the right valve off to the side (Figure 10).

CAUTION: Never hold the oyster in your hand while shucking it.

Orient your specimen so that the anterior end is pointed away from you. The dorsal and ventral sides of the oyster are determined by the internal anatomy. The dorsal side of the oyster is on your left, which is the location of the rectum and anus. The ventral side of the oyster is on your right, which is the location of the gills and mouth (Figure 11).

The mantle is a thin layer of tissue that lines the inner part of each valve. It contains glands that extract elements from the water and convert them to compounds that make up each valve. Calcium carbonate makes up about 98 percent of each valve, this is the same material used to make chalk.

[mantle video]

 View a 6 second video (1.6 MB, requires the free Quicktime plug-in).

Using a stereomicroscope observe the tentacles around the edge of the mantle (Figure 12).

[tentacle video]

 View a 10 second video (2.7 MB, requires the free Quicktime plug-in).


12. What is one function of the tentacles?
Capturing food     Locomotion     Sensory reception     Defense mechanism     Clear your answer


13. To what stimuli do you suppose they are responsive?
Light     Vibration     Salinity     Temperature
All of these     None of these     Clear your answer

Carefully fold back or cut the mantle on the ventral side.
Figure 13 - Sliding a probe underneath the mantle.
Figure 14 - Lifting the mantle.

Directly underneath the mantle are the gills. The gills are the largest organ of the oyster (Figure 15). Each gill consists of two folds of tissue. There are two points of attachment.
Figure 16 - one of the two points of attachement.
Figure 17 - The other point of attachment.

[gill video]

 View a 10 second video (2.7 MB, requires the free Quicktime plug-in).


14. How many gills are there?
2     4     6     Clear your answer


15. What are the functions of the gills?
digestion     gas exchange     producing new shell     moving water    
digestion & gas exchange     gas exchange & moving water     moving water & producing new shell     Clear your answer


16. Locate the two points of attachment for the gills.

The water which crosses the gills merges into the epibranchial chambers, then into the cloacal chamber which leads to the environment. Identify these structures by lifting the mantle at the posterior end and pulling it back over the adductor muscle.

The adductor muscle, which contains two types of fibers comprising the translucent and white portions, is located toward the posterior end and is below the visceral mass. The weight of this muscle accounts for 20-40 percent of the soft tissue weight of the oyster! You know about its strength if you tried to open a living specimen (Figure 18).


17. Locate the adductor muscle.

For the next parts of the laboratory it is desirable to remove the right (top) mantle. Cut carefully around the adductor muscle and at the point of attachment to the body and remove it (if you need help, go back to the instructions and look at Figure 13 and Figure 14).

The heart lies in the pericardial cavity anterior to the adductor muscle.
Figure 19a - The heart in the pericardium.
Figure 19b - Exposing the heart.
Figure 19c - The heart with the pericardial covering removed.
Figure 19d - Close-up of the heart.


18. Locate the heart.


19. How many atria are present?
1     2     3     Clear your answer


20. How many ventricles are present?
1     2     3     Clear your answer


21. Do oysters have an open or closed circulatory system?
Open system - An open circulatory consists of veins, arteries and sinuses or open cavities.
Closed system - A closed circulatory consists of veins, arteries and capillaries.
open     closed     Clear your answer

Bonus: How does the oyster heart and circulatory system compare to your heart and circulatory system?

With the mantle removed follow the pathway of the digestive organs.
Figure 20 - Locating the digestive gland.
Figure 21 - Locating the labial palps, mouth, rectum and anus.


22. Locate the following structures (Figure 22):
  • Labial Palps
  • Mouth
  • Esophogus
  • Stomach
  • Digestive Gland
  • Intestine
  • Rectum
  • Anus