The septal and pharyngeal nephridia open into alimentary canal and are of enteronephric type. It is an adaptation for

Options

A. Conservation of water ( osmoregulation )
B. Conservation of heat
C. Regulation of temperature
D. Regulation of amino acids .

Answer

### Step-by-Step Solution:

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

2. **Types of Nephridia**: In annelids, there are different types of nephridia, including septal, pharyngeal, and integumentary nephridia. The septal and pharyngeal nephridia are specifically noted for their connection to the alimentary canal.

3. **Enteronephric Type**: The term "enteronephric" refers to nephridia that open into the gut (alimentary canal). This adaptation allows for the excretion of waste directly into the digestive system.

4. **Function of Enteronephric Nephridia**: The primary function of these nephridia is to facilitate the removal of waste while also allowing for the reabsorption of water. This is crucial for maintaining water balance in the organism.

5. **Osmoregulation**: The adaptation of having enteronephric nephridia helps in osmoregulation, which is the process of regulating water and electrolyte balance in the body. By reabsorbing water from the waste before it is excreted, the organism conserves water.

6. **Conclusion**: Therefore, the adaptation of septal and pharyngeal nephridia opening into the alimentary canal is primarily for the conservation of water through osmoregulation.