Define haemocoel.

Explanation

**Step-by-Step Text Solution:**

1. **Understanding the Term:** The term "haemocoel" refers to a specific type of body cavity found in certain organisms.

2. **Identifying Organisms:** Haemocoel is primarily found in most invertebrates, which are animals that lack a backbone. This includes various groups such as arthropods and mollusks.

3. **Function of Haemocoel:** The haemocoel serves as a space that contains the circulatory fluid, which is typically blood. This fluid plays a crucial role in transporting nutrients, gases, and waste products throughout the organism's body.

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