Define heamocoel.

Explanation

**Step-by-Step Solution:**

1. **Definition of Hemocoel**: Hemocoel is a type of body cavity that is filled with blood. It is considered a "false" coelom because, unlike true coeloms found in coelomates (organisms with a true body cavity), hemocoel does not have a lining of mesodermal tissue that completely surrounds it.

2. **Location and Composition**: In organisms that possess a hemocoel, the cavity is situated within the mesoderm. This means that while the mesoderm is present, it does not fully enclose the hemocoel as seen in true coelomates.

3. **Presence in Arthropods**: Hemocoel is primarily found in arthropods, which include insects, arachnids, and crustaceans. This is a distinctive feature of these organisms.

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