One very special feature in the earthworm is that

Options

A. a) fertilisation of eggs occurs inside the body
B. b) the typhlosole greatly increases the effective absorption area of intestine
C. c) the S-shaped setae embedded in the integument are the defensive weapons used against the enemies
D. d) it has a long dorsal tubular heart

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for a special feature of the earthworm. We need to evaluate the provided options to identify the correct one.

2. **Analyzing Option A**:
- Option A states that fertilization of the eggs occurs inside the body.
- This is incorrect because in earthworms, fertilization occurs outside the body, specifically in the soil where both ova and sperm are deposited.

3. **Analyzing Option B**:
- Option B claims that the typhlosole greatly increases the effective absorption area of the intestine.
- The typhlosole is indeed an internal median fold located between the 26th and 35th segments of the earthworm's body. It increases the surface area for absorption of nutrients in the intestine, making this statement correct.

4. **Analyzing Option C**:
- Option C suggests that S-shaped setae embedded in the integument are defensive weapons against enemies.
- This is incorrect because setae are primarily used for locomotion, not as defensive weapons.

5. **Analyzing Option D**:
- Option D states that the earthworm has a long dorsal tubular heart.
- This is also incorrect as earthworms have a segmented heart, not a long tubular heart.

6. **Conclusion**: After evaluating all options, the correct answer is Option B, which states that the typhlosole greatly increases the effective absorption area of the intestine.

**Final Answer**: The very special feature in the earthworm is that the typhlosole greatly increases the effective absorption area of the intestine.

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