The dorsal side of the skin of Pheretima is brown due to

Options

A. Porphyrin
B. Melanin
C. Heparin
D. Renin

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the reason for the brown coloration on the dorsal side of the skin of the earthworm Pheretima.

2. **Identifying the Pigment**: The brown color on the dorsal side of the earthworm is due to the presence of a specific pigment.

3. **Naming the Pigment**: The pigment responsible for this coloration is called **porphyrin**.

4. **Function of Porphyrin**: Porphyrin not only provides the brown coloration but also serves a protective function. It helps protect the skin of the earthworm from harmful ultraviolet (UV) rays emitted by the sun.

5. **Distinguishing from Other Pigments**: It is important to note that while other pigments like melanin are found in humans and serve to provide skin coloration, porphyrin is specifically associated with earthworms and has additional functions.

6. **Conclusion**: Therefore, the correct answer to the question is that the brown coloration of the dorsal side of the skin of Pheretima is due to the presence of **porphyrin**.

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