__________ is/are absent in Echinoderms but present in mollusca

Options

A. Larval stage
B. Flame cells
C. Locomoty organs
D. Excretory organs

Answer

To answer the question "__________ is/are absent in Echinoderms but present in Mollusca," we will analyze the characteristics of both Echinoderms and Mollusca step by step.

### Step-by-Step Solution:

1. **Understanding Echinoderms and Mollusca**:
- Echinoderms (e.g., starfish, sea urchins) and Mollusca (e.g., snails, clams) are both groups of invertebrates.
- They have different anatomical and physiological features.

2. **Identifying the Options**:
- The question provides several options to consider, including larval stages, flame cells, locomotory organs, and excretory organs.

3. **Analyzing Larval Stages**:
- Both Echinoderms and Mollusca have larval stages. For example, Echinoderms have Bipinaria larvae, while Mollusca have Trochophore larvae.
- Therefore, larval stages are not the correct answer.

4. **Analyzing Flame Cells**:
- Flame cells are excretory structures found in Platyhelminthes (flatworms), not in either Echinoderms or Mollusca.
- Hence, flame cells are not relevant to this question.

5. **Analyzing Locomotory Organs**:
- Echinoderms possess tube feet as locomotory organs, while Mollusca have a muscular foot for movement.
- Thus, locomotory organs are present in both groups, making this option incorrect.

6. **Analyzing Excretory Organs**:
- Mollusca have a well-developed excretory system, typically using structures called nephridia (which function like kidneys).
- In contrast, Echinoderms do not have a specialized excretory system; they lack primary excretory organs and excrete waste primarily through their respiratory system.
- Therefore, excretory organs are absent in Echinoderms but present in Mollusca.

7. **Conclusion**:
- The correct answer to the question is "Excretory organs."

### Final Answer:
**Excretory organs** are absent in Echinoderms but present in Mollusca.