Madreporite is associated with
(a) Water vascular system
(b) Canal system
(c) Blood vascular system
(d) Digestive system.

Options

A. Water vascular system
B. Canal system
C. Blood vascular system
D. Digestive system.

Answer

To solve the question "Madreporite is associated with:", we will analyze the options provided and determine the correct association based on our knowledge of echinoderms.

### Step-by-Step Solution:

1. **Understanding Madreporite**:
- The madreporite is a specialized structure found in echinoderms, particularly in starfish (also known as sea stars). It serves as an entry point for water into the water vascular system.

2. **Identifying the Water Vascular System**:
- The water vascular system is a unique feature of echinoderms. It is a network of fluid-filled canals that plays a crucial role in locomotion, feeding, and gas exchange.

3. **Analyzing the Options**:
- (a) Water vascular system: This is the system that the madreporite is directly associated with, as it regulates the flow of water into the system.
- (b) Canal system: While the madreporite is part of the canal system, it is specifically associated with the water vascular system.
- (c) Blood vascular system: Echinoderms do not have a true blood vascular system like other animals, so this option is incorrect.
- (d) Digestive system: The madreporite is not involved in digestion, making this option incorrect as well.

4. **Conclusion**:
- Based on the analysis, the correct answer is (a) Water vascular system. The madreporite is essential for the functioning of this system in echinoderms.

### Final Answer:
(a) Water vascular system