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[Oyster Anatomy Laboratory]


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


Sturdy gloves
Large magnifying glass
Dissecting kit
Paper towels



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).

[Introduction] [External Laboratory] [Internal Laboratory] [Aquarium Set-up] [Glossary]
[Bibliography] [Teacher Resources 5E] [Acknowledgements]

This page was last updated on April 20, 2000

This page is part of the Maryland Sea Grant Oyster web site.

For more information, report problems or provide comments,
please contact:

Maryland Sea Grant
0112 Skinner Hall
College Park, MD 20742
Phone: (301) 405-6379
Email: mdsg@mdsg.umd.edu
Web: www.mdsg.umd.edu

[Maryland Sea Grant]