Which one of the following are pseudocoelomates ?

Options

A. Nematodes
B. Trematodes
C. Sponges
D. Echinoderms

Explanation

To determine which of the given options are pseudocoelomates, we need to understand the definitions and classifications of body cavities in animals. Here’s a step-by-step solution:

### Step 1: Understand the Types of Body Cavities
- **Coelom**: A true body cavity that is fluid-filled and located between the body wall and the digestive tract. Organisms with true coeloms are called **coelomates**.
- **Pseudocoelom**: A false body cavity that is not completely lined with mesoderm. Organisms with pseudocoeloms are called **pseudocoelomates**.
- **Acoelomates**: Organisms that do not have any body cavity.

### Step 2: Analyze the Given Options
1. **Nematodes**: These are roundworms that possess a pseudocoelom. Therefore, they are classified as pseudocoelomates.
2. **Termitodes**: These belong to the phylum Platyhelminthes (flatworms), which are acoelomates. Hence, they are not pseudocoelomates.
3. **Sponges**: Sponges belong to the phylum Porifera and are also acoelomates. Thus, they are not pseudocoelomates.
4. **Echinoderms**: These organisms (like starfish and sea urchins) have a true coelom. Therefore, they are coelomates and not pseudocoelomates.

### Step 3: Conclusion
Based on the analysis, the only organism from the options that is classified as a pseudocoelomate is **Nematodes**.

### Final Answer
The correct answer is **Nematodes**.

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