Name: _________________________
Date: __________________________
Clam Dissection
Introduction:
A clam lives between two shells, or valves, making it a member of the class Bivalvia. The shell
is made up of calcium carbonate that is secreted by the animal’s mantle. It is a slow moving
organism and spends much of its life buried in the sand. It is a filter feeder and relies on the
microscopic plankton suspended in the water it lives in. The body of the clam is enclosed in a
shell consisting of two valves, hinged dorsally.
Procedure: You can find the answers to many of these questions by following along in the
appropriate section of the lab manuals or in your textbook.
1. Fill in the blanks below to identify the clam’s anterior, posterior, ventral, and dorsal regions.
2. Examine the external surface of the shell. Locate the large knob at the dorsal surface. This
area is called the umbo. Why is this area important to the clam?
3. Insert the dissecting scissors between the two shells and cut the anterior and posterior
adductor muscles. Looking at the inside of the shell reveals more about the clam. A hinge,
made up of intermeshing teeth, forms the joint between the valves. The tough, but pliable hinge
ligament holds the two valves together. The adductor muscle scars show where these important
muscles were once attached. What is the function of the two adductor muscles?
The Pallial line is where the mantle attaches to the shell.
4. Label the following structures on the picture below (the pointers have been drawn for you):
hinge joint, umbo, Pallial line, and the two adductor muscles.
5. Now look at some of the other organs of the clam. The large, muscular foot can reach outside
the shell so that the clam can burrow. The foot retractor muscles, as well as the muscles in the
foot itself, control the foot. Water comes into the clam through the incurrent siphon and leaves
through the excurrent siphon.
Together, these openings make up what we call the "neck" of the clam. The clam sits buried in
sediment, and sticks its “neck” up into the water above so that it can suck in and release water.
The water that the clam sucks in through the incurrent siphon contains oxygen and food
(plankton). The water that the clam releases through the excurrent siphon contains the animal's
waste products, including carbon dioxide and undigested food.
6. The mantle is the part of the animal that forms the shell. The mantle secretes calcium
carbonate, the compound that we see as the hard substance that makes up seashells.
7. The clam's gills serve several important functions: obtaining oxygen and getting food.
8. Label the picture below using the following terms: Adductor muscles, excurrent siphon,
incurrent siphon, mantle, foot, and gills.
9. Locate the labial palps, two flap-like appendages that encircle the mouth. Spread them apart
to view the mouth. The labial palps move the food on toward the mouth. Food particles move
from the mouth and esophagus to a multi-chambered stomach with numerous passageways. This
is followed by a large intestine that ends at the anus near the excurrent siphon.
10. The clam has an "open" circulatory system, so that once the blood gets to the outer tissues, it
leaves the blood vessels and flows into open sinuses, or cavities, where it directly bathes the
tissues. Locate the heart and pericardial cavity of the clam. In contrast, in our circulatory
systems, blood always stays in some kind of blood vessel, such as capillaries. Then it collects in
the open space of the pericardium. Next, the blood returns to the heart, and the cycle starts all
over again.