Locomotion occurs in Sandworm or Nereis through
(a) Chaetae
(b) Setae
(c) Legs
(d) Parapodia

Options

A. Chaetae
B. Setae
C. Legs
D. Parapodia

Answer

To solve the question regarding the locomotion in Sandworm or Nereis, we will analyze the options provided:

1. **Understanding the Organism**:
- Nereis, commonly known as sandworm, belongs to the phylum Annelida. Annelids are segmented worms that have specialized structures for locomotion.

2. **Evaluating the Options**:
- **(a) Chaetae**: This term refers to bristle-like structures found in annelids, but they are not the primary structures for locomotion.
- **(b) Setae**: Setae are indeed present in annelids and assist in locomotion, but they are part of a larger structure.
- **(c) Legs**: Annelids do not have legs; they have a different mode of locomotion.
- **(d) Parapodia**: These are paired, lateral extensions found on each segment of the body of Nereis. Parapodia are crucial for movement in aquatic environments and help in swimming and crawling.

3. **Conclusion**:
- The correct answer is **(d) Parapodia**. They are the primary structures responsible for locomotion in sandworms or Nereis.

### Step-by-Step Solution:
1. Identify the organism in question (Nereis or sandworm).
2. Understand that Nereis belongs to the phylum Annelida.
3. Analyze each option provided for locomotion structures.
4. Determine that parapodia are the main structures aiding locomotion in Nereis.
5. Conclude that the correct answer is **(d) Parapodia**.