Left, a geoduck, Panopea generosa, of the Pacific Northwest. Geoducks can grow to 8 inches, weigh over 5 lbs, and live 150 years. Center, Ocean quahog, Arctica islandica. A recently collected specimen has a verified age of 220 years, making it the oldest known living animal. Right, the giant ocean clam, Tridacna gigas. This clam can grow to four feet in length, weigh 500 pounds, and, like corals, get up to 90% of their energy from symbiotic zooxanthellae.
Marine Science - Mr. Black
Pre-lab due 2/16; analysis items & labeled drawing due 2/22. No formal write-up due.
The phylum Mollusca includes snails, clams, chitons, slugs,
limpets, octopi, and squid. As mollusks develop from a fertilized egg
to an adult, most pass through a larval stage called the trocophore.
The trocophore is a ciliated, free-swimming stage. Mollusks also have
a radula or file-like organ for feeding, a mantle that may secrete a
shell, and a muscular foot for locomotion. Clams are marine mollusks
with two valves or shells. Like all mollusks, a clam has a mantle
which surrounds its soft body. It also has a muscular foot which
enables the clam to burrow itself in mud or sand. The soft tissue
above the foot is called the visceral mass and contains the clam's
To study the internal and external anatomy of a bivalve
Dissecting pan, dissecting kit, screwdriver, lab apron, safety
glasses, fresh clam
- Give the kingdom, phylum, and class for the clam.
- Give several examples of species of clam.
- What clam species is most commonly found in waters off the coast of Sarasota?
- What is the mantle? What is its function?
- What controls the opening and closing of the clam's
- How do clams move?
- How do clams feed?
- Why are clams called bivalves?
- Put on your lab apron, safety glasses, and plastic
- Place a clam in a dissecting tray and identify the anterior
and posterior ends of the clam as well as the dorsal, ventral,
& lateral surfaces.
- Locate the umbo, the bump at the anterior end of the valve.
This is the oldest part of the clam shell. Find the hinge ligament
which hinges the valves together and observe the growth
- Turn the clam with its dorsal side down and insert a
screwdriver between the ventral edges of the valves. Carefully
work the tip of the screwdriver between the valves so you do not
jab your hand.
- Turn the screwdriver so that the valves are about a centimeter
apart. Leave the tip of the screwdriver between the valves and
place the clam in the pan with the left valve up.
- Locate the adductor muscles. With your blade pointing toward
the dorsal edge, slide your scalpel between the upper valve &
the top tissue layer. Cut down through the anterior adductor
muscle, cutting as close to the shell as possible.
- Repeat step 6 in cutting the posterior adductor muscle.
- Bend the left valve back so it lies flat in the tray.
- Run your fingers along the outside and the inside of the left
valve and compare the texture of the two surfaces.
- Examine the inner dorsal edges of both valves near the umbo
and locate the tooth like projections. Close the valves &
notice how the tooth like projections interlock.
- Locate the muscle "scars" on the inner surface of the left
valve. The adductor muscles were attached here to hold the clam
- Identify the mantle, the tissue that lines both valves &
covers the soft body of the clam. Find the mantle cavity, the
space inside the mantle.
- Locate two openings on the posterior end of the clam. The more
ventral opening is the incurrent siphon that carries water into
the clam and the more dorsal opening is the excurrent siphon where
wastes & water leave.
- Using scissors and your index finger, carefully remove the half of the mantle that
lined the left valve. After removing this part of the mantle, you
can see the gills, respiratory structures.
- Observe the muscular foot of the clam, which is ventral to the
gills. Note the hatchet shape of the foot used to burrow into mud
- Locate the palps, flap like structures that surround &
guide food into the clam's mouth. The palps are anterior to the
gills & ventral to the anterior adductor muscle. Beneath the
palps, find the mouth.
- With scissors, cut off the ventral portion of the foot. Use
the scalpel to carefully cut the muscle at the top of the foot
into right and left halves.
- Carefully peel away the muscle layer to view the internal
- Locate the spongy, yellowish reproductive organs.
- Ventral to the umbo, find the digestive gland, a greenish
structure that surrounds the stomach.
- Locate the long, coiled intestine extending from the
- Follow the intestine through the calm. Find the area near the
dorsal surface that the intestine passes through called the
pericardial area. Find the clam's heart in this area.
- Continue following the intestine toward the posterior end of
the clam. Find the anus just behind the posterior adductor
- Use your probe to trace the path of food & wastes from the
incurrent siphon through the clam to the excurrent siphon.
- Answer the questions on your lab report & label the
diagrams of the internal structures of the clam. Also, use arrows
on the clam diagram to trace the pathway of food as it travels to
the clam's stomach. Continue the arrows showing wastes leaving
through the anus.
Figure 1. Some external anatomy of the clam.
Figure 2. Clam anatomy.
When you have finished dissecting the clam, dispose of the clam in the trash and clean, dry, and return all dissecting
equipment to the top right-hand drawer of your lab station. Wash your hands thoroughly with soap and water before leaving lab.
Clam Dissection Questions
- What is the oldest part of a clam's shell called and how can
it be located?
- What do the rings on the clam's shell indicate? How old is the clam you are working with?
- What is the function of the tooth like projections at the
dorsal edge of the clam's valves?
- Where is the mantle located in the clam?
- What is the mantle cavity?
- Where are the incurrent & excurrent siphons located and
what is their function?
- Describe O2 - CO2 exchange in clams.
- Describe the shape of the clam's foot.
- Where are the palps found and what is their function?
- Describe in detail the movement of food from the incurrent siphon through
the digestive system to the excurrent syphon.
- Where is the clam's heart located?
- Why are clam's referred to as "filter feeders"?
- Print out, label, and glue into your lab book, the internal
structures of the clam and draw arrows showing the pathway of food
as it travels to the clam's stomach. Also, use arrows on the clam
diagram to trace the pathway of food as it travels to the clam's
stomach. Continue the arrows showing wastes leaving through the
here for photos and practice quiz.