Leech secretes which of the following anticoagulant

Options

A. (a) Hirudin
B. (b) Heparin
C. (c) Serotonin
D. (d) Histamine

Answer

### Step-by-Step Solution:

1. **Identify the Organism**: The question asks about leeches, which are blood-sucking worms belonging to the phylum Annelida.

2. **Understand the Function of Leeches**: Leeches have a specialized function of feeding on the blood of their hosts. To facilitate this, they need to prevent blood clotting.

3. **Identify the Anticoagulant**: Leeches secrete a specific anticoagulant to prevent blood from clotting while they feed. This anticoagulant is crucial for their feeding process.

4. **Examine the Options**:
- **Option A: Hirudin**: This is an anticoagulant found in the salivary glands of leeches. It inhibits thrombin, which is essential for blood clotting.
- **Option B: Heparin**: This is another anticoagulant, but it is found in humans, not in leeches.
- **Option C: Serotonin**: This is a neurotransmitter that affects mood and cognition, not an anticoagulant.
- **Option D: Histamine**: This is involved in inflammatory responses and is secreted by white blood cells in humans, not an anticoagulant.

5. **Determine the Correct Answer**: Based on the analysis of the options, the correct anticoagulant secreted by leeches is **Hirudin**.

### Final Answer:
The leech secretes **Hirudin** as its anticoagulant.