Gas exchange surface of Earthworm is

Options

A. tracheae
B. gills
C. skin
D. ctenidia

Answer

**Step-by-Step Solution:**

1. **Identify the Organism**: The question asks about the gas exchange surface of an earthworm. Earthworms belong to the phylum Annelida.

2. **Understand the Structure**: Earthworms have a segmented body structure, which means their skin is also segmented.

3. **Respiratory Organs**: Unlike many animals that have specialized respiratory organs (like lungs or gills), earthworms do not possess such structures.

4. **Mechanism of Gas Exchange**: Earthworms perform gas exchange primarily through their skin. They absorb oxygen and expel carbon dioxide directly through their moist skin.

5. **Evaluate the Options**:
- **Option A: Trachea** - Incorrect, as trachea is not found in earthworms.
- **Option B: Gills** - Incorrect, as gills are respiratory organs found in aquatic animals like fish, not earthworms.
- **Option C: Skin** - Correct, as the skin is the surface through which gas exchange occurs in earthworms.
- **Option D: Tinnidia** - Incorrect, as tinnidia are respiratory structures found in mollusks.

6. **Conclusion**: The gas exchange surface of the earthworm is the skin.

**Final Answer**: The gas exchange surface of the earthworm is the skin.

---