Open circulatory system is found in ______ where coelomic cavity is filled with blood.

Explanation

### Step-by-Step Solution:

1. **Understanding the Open Circulatory System**: An open circulatory system is a type of circulatory system where the blood is not confined to blood vessels. Instead, it flows freely in the body cavity, bathing the organs directly.

2. **Identifying Organisms with Open Circulatory Systems**: This system is commonly found in certain groups of animals, particularly in invertebrates.

3. **Recognizing the Phylum**: The primary group of organisms that exhibit an open circulatory system is the phylum Arthropoda. This includes insects, arachnids, and crustaceans.

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