Which among the following does not help in the locomotion of aquatic annelids?

Options

A. Circular muslces
B. Parapodia
C. Nephridia
D. Logitudinal muslces

Explanation

To determine which among the following does not help in the locomotion of aquatic annelids, we will analyze each option provided:

1. **Circular Muscles**:
- Annelids have circular muscles that contract and help in the elongation and movement of their bodies. These muscles are essential for locomotion as they allow the body to change shape and move through water.

2. **Parapodia**:
- Parapodia are lateral appendages found in some annelids, particularly polychaetes. They assist in swimming and crawling, thus playing a significant role in locomotion.

3. **Nephridia**:
- Nephridia are excretory organs in annelids that help in the removal of nitrogenous waste from the body. They are not involved in locomotion.

4. **Longitudinal Muscles**:
- Longitudinal muscles work in conjunction with circular muscles to facilitate movement. They help in shortening and thickening the body, aiding in locomotion.

After analyzing all the options, we conclude that **nephridia** does not help in the locomotion of aquatic annelids.

### Final Answer:
**Nephridia**