Which is correct about nematocyst in Hydra

Options

A. It is re-used
B. Ejection is conditioned reflex
C. Ejection occurs in response to contact and pierces the prey
D. Prevents coming in contact with other Hydra.

Answer

To answer the question "Which is correct about nematocyst in Hydra?", we will analyze the characteristics and functions of nematocysts in Hydra step by step.

### Step-by-Step Solution:

1. **Understanding Nematocysts**:
- Nematocysts are specialized cells found in members of the phylum Cnidaria, including Hydra. They are commonly referred to as stinging cells.

2. **Location of Nematocysts**:
- These cells are located in the outer epithelial layer of the Hydra's body wall.

3. **Mechanism of Action**:
- Nematocysts are triggered by mechanical or chemical stimuli. When stimulated, they release a coiled thread that can inject toxins into a prey or potential threat.

4. **Reusability of Nematocysts**:
- Once a nematocyst is discharged, it cannot be reused. The thread is expelled to pierce the prey, and the cell must regenerate a new nematocyst.

5. **Stimuli for Discharge**:
- The discharge of nematocysts occurs in response to stimuli such as touch or other chemical signals, not as a conditioned reflex.

6. **Correct Answer**:
- Based on the analysis, the correct statement regarding nematocysts in Hydra is that they are triggered by stimuli and are not reusable after discharge.

### Conclusion:
The correct option about nematocysts in Hydra is that they are discharged in response to stimuli and cannot be reused.