Excretory organ in annelida origin

Options

A. Ectoderm
B. Mesoderm
C. Endodem
D. All the above

Answer

### Step-by-Step Solution:

1. **Understanding Annelida**: Annelida refers to a phylum of segmented worms. These organisms exhibit metameric segmentation, meaning their bodies are divided into repeated segments.

2. **Excretory Structures**: The primary excretory structures in Annelida are called nephridia. Nephridia are ciliated, tube-like structures that facilitate the removal of waste from the body.

3. **Origin of Nephridia**: The question asks about the origin of these excretory organs. In Annelida, nephridia originate from the ectoderm, which is the outermost layer of cells in the embryo.

4. **Ectoderm vs. Other Layers**:
- The ectoderm is responsible for forming structures on the outer surface of the body, including the excretory organs.
- The mesoderm, which lies between the ectoderm and endoderm, primarily gives rise to muscles and blood vessels, not excretory organs.
- The endoderm is the innermost layer that forms internal organs, such as the digestive system, but not the excretory system.

5. **Conclusion**: Therefore, the excretory organs in Annelida originate from the ectoderm. This is the correct answer to the question.