The fresh water animal is
(a) Tubifex
(b) Polynoe
(c) Pontobdella
(d) Neanthes

Options

A. Tubifex
B. Polynoe
C. Pontobdella
D. Neanthes

Answer

To determine which of the given organisms is a freshwater animal, we will analyze each option step by step.

### Step 1: Analyze the options
We have four options to consider:
- (a) Tubifex
- (b) Polynoe
- (c) Pontobdella
- (d) Neanthes

### Step 2: Identify the habitat of each organism
1. **Neanthes**: This organism is primarily marine. It is not found in freshwater environments. Therefore, it cannot be the correct answer.

2. **Polynoe**: Polynoe is also a marine organism. It is typically found in oceanic waters and does not inhabit freshwater. Thus, this option is also incorrect.

3. **Pontobdella**: Similar to the previous two, Pontobdella is exclusively marine. It does not live in freshwater habitats, so this option is not correct either.

4. **Tubifex**: Tubifex is known as a freshwater worm, often referred to as a sludge worm or sewage worm. It is commonly found in the sediments of lakes and rivers, making it a true freshwater organism.

### Step 3: Conclusion
After analyzing all the options, we find that:
- The correct answer is **(a) Tubifex**, as it is the only organism listed that is a freshwater animal.

### Final Answer:
The freshwater animal is **(a) Tubifex**.

---