Ctenidia of mollucsa helps in

Options

A. Respiration
B. Excretion
C. 1 and 2
D. Locomotion

Answer

### Step-by-Step Solution:

1. **Understanding Ctenidia**: Ctenidia are specialized structures found in mollusks, which are aquatic animals like snails, clams, and octopuses. They are essentially gill-like structures.

2. **Function of Ctenidia**: The primary function of ctenidia is to facilitate respiration. They are involved in the exchange of gases, allowing the organism to take in oxygen and expel carbon dioxide.

3. **Structure of Ctenidia**: Ctenidia are complex outgrowths of the mantle, which is the tissue that covers the mollusk's body. Their structure increases the surface area available for gas exchange, making respiration more efficient.

4. **Evaluating Options**:
- **Option 1: Respiration** - This is the correct answer since ctenidia are primarily involved in the respiratory process.
- **Option 2: Excretion** - This is incorrect because the excretory organs in mollusks are called nephridia, not ctenidia.
- **Option 3: First and Second** - This option is also incorrect because it combines the two wrong options.
- **Option 4: Locomotion** - This is incorrect as well; locomotion in mollusks is primarily carried out by the muscular foot, not ctenidia.

5. **Conclusion**: Based on the analysis, the correct answer is that ctenidia of mollusks help in respiration.