What are the excretory organs of flat worms, annelids, crustaceans, insects and spiders?

Explanation

To answer the question regarding the excretory organs of flatworms, annelids, crustaceans, insects, and spiders, we can break it down step by step:

### Step-by-Step Solution:

1. **Flatworms**:
- Flatworms belong to the phylum Platyhelminthes.
- Their excretory system is primitive and is known as **Proto-nephridia**.
- These structures help in the removal of waste products from the body.
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