Name the first animal group to have blood-vascular system

Explanation

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the first animal group that developed a blood-vascular system. This system is essential for transporting nutrients, gases, and waste products throughout the body.

2. **Identifying Animal Groups**: To answer this question, we need to consider various animal groups and their evolutionary development. The blood-vascular system is a significant advancement in the evolution of animals.

3. **Recognizing the Phylum**: The first animal group to have a well-developed blood-vascular system is found in the phylum Annelida. This phylum includes segmented worms, such as earthworms.

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