Pipi Dissection

Topic

The external and internal anatomy of a pipi (clam) is typical of bivalves.

Introduction

Molluscs are some of the most common marine invertebrates. All molluscs have several characteristic features, which include a tissue called the mantle. Molluscs are divided into three groups: cephalopods (octopus and squid), gastropods (snails and slugs), and bivalves (clams and mussels).

Bivalves have two shells, or valves, that protect their soft body parts. The shells hinge on one side and are held together by strong muscles. Clams are bivalves that spend most of their time lying on the seafloor. When frightened, a clam uses its wedge-shaped, muscular foot to burrow into the sediment. The clam foot can also help a clam move across the sediments. The soft tissue located just above the foot, the visceral mass, contains a clam’s organs. Clams get their nutrition by filtering food particles from water. Fresh sea water is supplied through an incurrent siphon. Water leaves the clam’s body and returns to the sea through an excurrent siphon.

In this experiment, you will examine the anatomy of a pipi (clam).

What’s Going On?

Clams are soft-bodied animals whose internal organs are protected by two shells. Like all molluscs, clams have a mantle. Located inside the mantle cavity are the digestive, respiratory, circulatory, reproductive, and nervous systems. Organs in all of these systems are visible, except for those of the nervous system.

As filter feeders, clams collect tiny particles of food suspended in the water. Water is continuously drawn in through an incurrent siphon and circulated over the gills. Food particles stick to mucus that coats this respiratory organ. Cilia, tiny hair-like structures, sweep the food particles towards the clam’s mouth. Food is digested in the stomach and intestine. Wastes of digestion are excreted through the anus, and filtered water is returned to the sea by the excurrent siphon.

Results and Analysis: Complete questions in your workbook. Integrate question and answer.

1.How many growth ring did you count? Generally pipis produce 2 growth rings each year. What was the age of your pipi?

2.Why are clams called bivalves?

3. What is the oldest part of the clam shell?

4. How do clams open and close their shells?

5. How does a clam draw water into its mantle cavity? What is the purpose of this behaviour?

6. Describe the shape of a clam’s foot and explain how the clam uses it for movement.

7. What is meant by the term “filter feeding”? How do clams filter feed?

8. Describe the path of a food particle through a clam’s body, beginning at the point where it is drawn in the incurrent siphon and ending at the anus.