In which animal, nerve cell is present but brain is absent ?

Options

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

Explanation

To answer the question "In which animal, nerve cell is present but brain is absent?", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks for an animal that has nerve cells (neurons) but does not possess a brain.

2. **Identify Animal Groups**: We need to consider various animal groups and their nervous systems. We can categorize animals based on their phyla.

3. **Evaluate Options**:
- **Sponges**: Belong to the phylum Porifera. They do not have a nervous system or neurons, so they do not fit the criteria.
- **Honey Bee and Cockroaches**: Both belong to the phylum Arthropoda. They possess a brain and a nervous system, so they do not fit the criteria.
- **Hydra**: Belongs to the phylum Coelenterata (or Cnidaria). Hydra does not have a centralized brain but does have nerve cells (neurons).

4. **Conclusion**: Among the options evaluated, Hydra is the only animal that has nerve cells but lacks a brain.

Thus, the answer is **Hydra**.