Which of the following occurs in molluscs but not in Echinoderms?

Options

A. Aristotle's lantern
B. Kidneys
C. Organ system level of organisation
D. Dioecious condition

Explanation

To determine which feature occurs in molluscs but not in echinoderms, we can analyze the characteristics of both groups step by step.

### Step-by-Step Solution:

1. **Identify the Groups**: We are comparing two groups: Mollusca (molluscs) and Echinodermata (echinoderms).

2. **List the Features**: We need to evaluate specific features or structures that may be present in one group and absent in the other.

3. **Evaluate Aristotle's Lantern**:
- Aristotle's lantern is a structure found in echinoderms, specifically in sea urchins, which aids in feeding (mastication).
- **Conclusion**: This feature is present in echinoderms but absent in molluscs.

4. **Evaluate Kidneys**:
- Molluscs possess a well-developed excretory system, including kidneys (nephridia).
- Echinoderms, on the other hand, do not have specialized excretory structures like kidneys; they excrete waste through their body surface.
- **Conclusion**: Kidneys are present in molluscs but absent in echinoderms.

5. **Evaluate Organ System Level of Organization**:
- Both molluscs and echinoderms exhibit an organ system level of organization.
- **Conclusion**: This feature is present in both groups.

6. **Evaluate Dioecious Condition**:
- Both molluscs and echinoderms can be dioecious (having distinct male and female individuals).
- **Conclusion**: This feature is present in both groups.

7. **Final Conclusion**: The only feature that occurs in molluscs but not in echinoderms is the presence of kidneys.

### Answer:
**Kidneys** occur in molluscs but not in echinoderms.

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