Which of the following use water from their environment as circulating fluid -

Options

A. Sponges
B. Coelenterates
C. a and b
D. Fishes

Answer

To determine which organisms use water from their environment as a circulating fluid, we can analyze the provided options step by step.

### Step 1: Understand the Role of Water in Circulation
Water serves as a medium for transporting nutrients, gases, and waste products in various organisms. Some organisms have specialized systems for this purpose, while others rely on the surrounding water directly.

### Step 2: Analyze the First Option - Sponges
- **Sponges** (Phylum Porifera) utilize a water canal system for circulation.
- Water enters through small openings called **ostea**.
- It then moves into a central cavity known as the **spongocoel**.
- Finally, the water exits through a larger opening called the **osculum**.
- This system allows sponges to filter nutrients and oxygen from the water, making them dependent on the surrounding water for circulation.

### Step 3: Analyze the Second Option - Cnidarians
- **Cnidarians** (e.g., jellyfish, corals) also use water as a circulating fluid.
- In these organisms, water enters through an opening called the **hypostome**, which functions similarly to a mouth.
- The water carries nutrients and gases, facilitating the exchange necessary for the organism’s survival.
- Cnidarians have a simple body plan that allows them to rely on the surrounding water for circulation and nutrient transport.

### Step 4: Conclusion
Both sponges and cnidarians utilize water from their environment for circulation. Therefore, the correct answer to the question is that both A (sponges) and B (cnidarians) use water as a circulating fluid.

### Final Answer
The correct option is: **Both A and B (Sponges and Cnidarians)**.

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