[MARYLAND SEA GRANT - OYSTERS IN THE CLASSROOM
[Oyster Anatomy Laboratory]

Internal Anatomy: Observation and Investigation

Materials:

This activity uses:
  • Live oysters
  • Dissecting tray or metal pie pan
  • Oyster knife
  • Sturdy gloves
  • Dissecting kit
  • Stereomicroscope (optional)
  • Large magnifying glass (optional)

Procedure

For centuries people have been devising ways to get the "meat" out of the oyster. These techniques are referred to as "shucking."

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

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

Hinge Method

Step 1: Place the oyster left value down on a hard surface with the umbo pointing toward you. Firmly hold down the oyster with a gloved hand.

Step 2: Insert the oyster knife in the hinge of the oyster (Figure 1).

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

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 3).

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

Orient the oyster 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 4).

Take A Closer Look: Examine the surface of the oyster body. If you carefully shucked the oyster you may be able to see the small Quenstedt muscle. (Figure 5). This muscle is proposed to be a foot (pedal) remnant from the larval form of the oyster. It was named after a German geologist and paleontologist Friedrich August von Quenstedt.

The mantle is a thin layer of tissue that lines the inner part of each valve (Figure 6). 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.

If available, use a stereomicroscope or magnifying glass to observe the tentacles around the edge of the mantle (Figure 7).

  2.   What is one function of the tentacles?
Capturing food     Locomotion     Sensory reception
Defense mechanism     Clear your answer
  3.   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 the mantle on the ventral side (Figure 8).

Directly underneath the mantle are the gills. They are the largest organ of the oyster (Figure 9). Each gill consists of two folds of tissue. There are two points of attachment.

  4.   Locate the two points of attachment for the gills.
Figure 10 - Anterior point of attachment
Figure 11 - Posterior point of attachment.

  5.   How many pairs of gills are there?
2     4     6     Clear your answer
  6.   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

The adductor muscle (Figure 12) is composed of two types of fibers - translucent and white Ᾱ and is located toward the posterior end of the oyster below the visceral mass and pericardial cavity (Figure 13). The weight of this muscle accounts for 20-40 percent of the soft tissue weight of an oyster! You know about its strength if you have ever tried to open a live oyster.

  7.   Locate the adductor muscle.

The heart is located in the pericardial cavity that is covered by a thin tissue called the pericardium (Figure 14).

  8.   Locate the heart by carefully removing the pericardium.
Figure 15 - Exposing the heart by removing the pericardium.
Figure 16 - Close-up of the heart.
  9.   How many atria are present?
1     2     3     Clear your answer

10.   How many ventricles are present?
1     2     3     Clear your answer
11.   Do oysters have an open or closed circulatory system?
open     closed     Clear your answer

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

Next follow the pathway of the digestive system. An oyster's digestive system consists of labial palps, mouth, esophogus, stomach, digestive gland, intestine, rectum, and anus.

There are two labial palps, one associated with each gill. Each are bilobed, ciliated and function to sort and transfer food from the gills to the mouth.


12.   Located of the labial palps (Figure 17).

Food is then passed from the mouth through a short esophogus to the stomach. The stomach is surrounded by the digestive gland that is the site for enzyme production and intracellular digestion.


13.   Locate of the digestive gland (Figure 18).

From the stomach undigested and digested materials are passed to the intestines where absorption of nutrients and further processing of wastes occurs. Waste products are passed onto the rectum exiting out the anus.

14.   Locate the rectum and anus (Figure 19).
15.   Locate the following structures (Figure 20):
  • Labial Palps
  • Mouth
  • Esophogus
  • Stomach
  • Digestive Gland
  • Intestine
  • Rectum
  • Anus
(for help see the sketch of oyster anatomy)