List the excretory organs of flatworms, annelids and crustaceans.

Explanation

To answer the question regarding the excretory organs of flatworms, annelids, and crustaceans, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Excretory Organs**:
- Excretory organs are specialized structures in organisms that are responsible for the removal of waste substances from the body.

2. **Identify Excretory Organs in Flatworms**:
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