Haemocoel is present in which group?

Answer

### Step-by-Step Solution:

1. **Understand the Term "Haemocoel":**
- Haemocoel is a type of body cavity found in certain organisms. It is part of the open circulatory system where blood (or hemolymph) is not confined to vessels.

2. **Identify the Characteristics of Haemocoel:**
- In organisms with a haemocoel, the blood (hemolymph) flows freely within the body cavity and comes into direct contact with tissues and organs. This system contrasts with a closed circulatory system, where blood is contained within vessels.

3. **Define Open Circulatory System:**
- An open circulatory system is one where the blood is not contained within blood vessels but instead bathes the organs directly in a cavity. This system is less efficient than a closed system but is sufficient for smaller organisms.

4. **Recognize Organisms with Haemocoel:**
- Organisms that possess a haemocoel include arthropods (such as insects, spiders, and crustaceans) and some mollusks.

5. **Conclude the Group:**
- Based on the characteristics and examples of organisms with a haemocoel, we conclude that the group in which haemocoel is present is **arthropods**.

### Final Answer:
Haemocoel is present in the group **Arthropoda**.

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