The two valves of Unio are hinged

Options

A. Dorsally
B. Ventrally
C. Anteriorly
D. Posteriorly.

Answer

To answer the question "The two valves of Unio are hinged," we can break down the solution into the following steps:

### Step-by-Step Solution:

1. **Understanding Unio**:
- Unio is a genus of freshwater bivalve mollusks, commonly known as freshwater mussels. They have two shells or valves that protect their soft body.

**Hint**: Remember that bivalves have two shells that serve as protective coverings.

2. **Identifying the Hinged Mechanism**:
- The two valves of Unio are connected by a hinge mechanism. This hinge allows the valves to open and close, which is essential for the mollusk's feeding and respiration.

**Hint**: Think about how a door opens and closes; the hinge allows for this movement.

3. **Locating the Hinge Position**:
- The hinge of the two valves in Unio is located on the dorsal side. This means that the two shells are hinged at the top, allowing them to swing open and closed.

**Hint**: Visualize the orientation of the bivalve; the dorsal side is typically the upper part.

4. **Understanding the Hinge Structure**:
- The hinge is supported by an elastic band known as the "hinge ligament." This ligament helps maintain the position of the valves and facilitates their movement.

**Hint**: Consider the hinge ligament as a rubber band that keeps the valves connected while allowing flexibility.

5. **Conclusion**:
- Therefore, the correct answer to the question is that the two valves of Unio are hinged dorsally.

**Hint**: Remember to focus on the dorsal position when identifying the hinge in bivalves.

### Final Answer:
The two valves of Unio are hinged dorsally.