The nephridia that open into gut are 

Options

A. open nephridia
B. closed nephridia
C. exonephric nephridia
D. enteronephric nephridia

Answer

**Step-by-Step Solution:**

1. **Understanding Nephridia**: Nephridia are excretory structures found in some invertebrates, including annelids like earthworms. They help in the removal of waste products from the body.

2. **Types of Nephridia**: There are different types of nephridia based on their structure and function:
- **Open Nephridia**: These nephridia have openings that allow waste to be excreted into the environment. They are often associated with adaptations for water conservation.
- **Closed Nephridia**: These are small-sized nephridia that do not have any openings. They are enclosed and typically do not directly connect to the external environment.
- **Exonephridia (Ectonephridia)**: These nephridia remove nitrogenous waste directly from the body to the external environment.
- **Entronephric Nephridia**: These nephridia open into the gut (intestine) and discharge waste through the excretory canal into the lumen of the intestine.

3. **Identifying the Correct Type**: The question specifically asks for the type of nephridia that open into the gut. Based on the definitions:
- Open nephridia do not open into the gut.
- Closed nephridia do not have openings.
- Exonephridia remove waste outside the body.
- Entronephric nephridia are the ones that open into the gut.

4. **Conclusion**: Therefore, the nephridia that open into the gut are called **Entronephric Nephridia**.

**Final Answer**: Entronephric Nephridia

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