What are locomotory organs in Nereis?

Explanation

### Step-by-Step Solution:

1. **Identify the Organism**: Nereis is a genus of marine polychaete worms that belong to the phylum Annelida and class Polychaeta.

2. **Locomotory Organs**: The locomotory organs in Nereis are primarily two structures: parapodia and setae.

3. **Parapodia**: Parapodia are paired, lateral appendages found on each segment of the Nereis. They play a crucial role in locomotion and are used for swimming and crawling.

...