Which of the following phylum has members which show presence of neurons but absence of brain ?

Options

A. Sponge
B. Earthworm
C. Cockroach
D. Hydra

Explanation

To determine which phylum has members that show the presence of neurons but the absence of a brain, we can analyze the options provided step by step:

### Step-by-Step Solution:

1. **Identify the Options**: The question provides four options related to different phyla: Sponges (Porifera), Earthworm (Annelida), Cockroach (Arthropoda), and Hydra (Cnidaria).

2. **Analyze Sponges (Porifera)**:
- Sponges are simple organisms that lack true tissues and organs.
- They do not have neurons or a brain.
- **Conclusion**: This option is incorrect.

3. **Analyze Earthworm (Annelida)**:
- Earthworms have a nervous system that includes a ventral nerve cord and a brain (cerebral ganglion).
- They possess neurons as well as a brain.
- **Conclusion**: This option is incorrect.

4. **Analyze Cockroach (Arthropoda)**:
- Cockroaches have a complex nervous system with a brain and a ventral nerve cord.
- They also possess neurons.
- **Conclusion**: This option is incorrect.

5. **Analyze Hydra (Cnidaria)**:
- Hydra has a simple nerve net and possesses neurons.
- However, it does not have a centralized brain structure.
- It exhibits a tissue level of organization without complex organs.
- **Conclusion**: This option is correct.

6. **Final Answer**: Based on the analysis, the correct phylum that has members showing the presence of neurons but absence of a brain is **Hydra, which belongs to the phylum Cnidaria**.