Bivalve: Anatomy & Reproduction

Instructor: Jeremy Battista

Jeremy has a master of science degree in education.

Bivalves are aquatic animals much lower on the evolutionary scale from humans, but a definite link exists along the way to our complex selves. Bivalve anatomy as well as their reproductive behavior provide a link between more simplistic animals and more complex, like humans. We will explore a little about bivalves here.

What Are Bivalves?

Bivalves, or Bivalvia, refer to a class of animals that live in freshwater and saltwater. They belong to the phylum Mollusca, which are more commonly called 'mollusks'. The name bivalve comes from Latin as most biological classifications do. 'Bi' means two and 'valve' is really 'valvae', which means 'leaves of a door'. So essentially, the bivalves are those with a two sided shell that will open and close via a hinge, like a door.

The first thing that might come to mind when you hear the word 'bivalve' is the common clam, oyster, or mussel. These are excellent examples of this class of animal as well as some of the most common.

Anatomical Features

The first characteristic of bivalves is two shells that open to reveal the animal itself. Inside of the shell is a lining of soft tissue called the mantle. This is the real 'meat' of the animal and the part that one would eat if eating a bivalve such as a clam. At the front and rear of the animal are anterior and posterior adductor muscles, respectively. These are responsible for holding the shell closed, similar to a human's adductor muscles in the legs. In humans, these allow you to bring your legs together.

Looking closely at the left side picture you can see two small ovals, one towards the front and one towards the back. This is where the adductor muscles attach.
Deepwater Bivalve

At the hinge of bivalve shells there is a ligament that allows the animal to open if it relaxes the adductor muscles. Near this ligament is a hinge with interlocking teeth. These help the shells stay lined up so they won't twist other ways. Finally, there is the pallial line, where the mantle attaches to the shell. This is simply where the soft tissue attaches to the shell. The features listed so far are the main features in common bivalves. Let's now discuss some of the more specific features found in most bivalves.

Within the mantle are a number of features that involve the daily life of the bivalve. For one, it secretes material that contributes to the shell growth of the animal. The mantle is also home to a muscular foot, used exactly how you might imagine a foot is used, for propulsion. The animal's gills are found here as well as its digestive system. Food comes in through the gills or sometimes through a siphon.

Here we see a pair of siphons sticking out from a clam.

The digestive system of a bivalve is fairly simple, similar to a worm's, a far cry from the human digestive system. An open circulatory system, heart, and nerves round out the main bulk of the mantle of the animal. Again, this is all enclosed inside of the shell.

Next let's focus on the reproductive system since the next section will cover bivalve reproduction. The gonads of bivalves are very close to the intestinal tract of the animal. Some are also hermaphroditic, possessing both male and female gonads, which is common in the more basic classes of animal. Most often, we see separate sexes in bivalves.


Even though bivalves make up a large class, they exhibit similar reproductive behaviors. Freshwater bivalves will 'free spawn' by releasing their sperm and eggs into the water. The eggs become fertilized in the water and develop as plankton, eventually growing into the animal itself. Many other bivalves will actually reproduce in some ways similar to humans. The male releases sperm into the water that the female then takes in while taking in water to eat. The sperm fertilize the female's eggs and larvae begin to form and grow. This happens inside of the female, until they reach a point where they are ready to be released.

To unlock this lesson you must be a Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use

Become a member and start learning now.
Become a Member  Back
What teachers are saying about
Try it now
Create an account to start this course today
Used by over 30 million students worldwide
Create an account