The body cavity of nemathelminthes is without peritoneal lining. It is

Options

A. Haemocoel
B. True coelom
C. Pseudocoel
D. Atrium

Answer

To solve the question regarding the body cavity of nemathelminthes (or nematodes) being without peritoneal lining, we will analyze the options provided and determine the correct answer step by step.

### Step 1: Understand the Body Cavity Types
The body cavity in animals can be classified into three main types:
1. **Coelom**: A true body cavity that is lined by mesodermal tissue (peritoneum).
2. **Pseudocoelom**: A body cavity that is not completely lined by mesodermal tissue; it has a lining that is derived from mesoderm but lacks a complete peritoneal lining.
3. **Acoelomate**: Animals that do not have a body cavity at all.

### Step 2: Analyze the Options
The options given are:
- Haemosoil
- True coelom
- Pseudocoel
- Atrium

#### Option Analysis:
- **Haemosoil**: This term refers to a fluid found in the circulatory system of some invertebrates, not a body cavity type.
- **True Coelom**: This is a body cavity fully lined by mesoderm, which is not the case for nematodes.
- **Pseudocoel**: This is a body cavity that is not lined by mesodermal cells completely, which aligns with the characteristics of nematodes.
- **Atrium**: This term generally refers to a chamber or cavity in the heart or other organs, not a type of body cavity.

### Step 3: Identify the Correct Answer
Given the definitions and analysis of the options, the body cavity of nemathelminthes is best described as a **pseudocoel**. This is because it is a body cavity that is not lined with a complete layer of mesodermal tissue, which is characteristic of nematodes.

### Conclusion
The correct answer to the question is **pseudocoel**.

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