On which basis, the phylum porifera is classified?

Explanation

**Step-by-Step Solution:**

1. **Understanding Phylum Porifera**: Phylum Porifera, commonly known as sponges, is a group of simple aquatic animals characterized by their porous bodies and lack of true tissues.

2. **Classification Basis**: The classification of Phylum Porifera is primarily based on the structure of their spicules, which are the skeletal elements found within the body of sponges.

3. **Identifying the Classes**: Phylum Porifera is divided into three main classes based on the composition of their spicules:
- **Class Hexactinellida**: This class is characterized by spicules that are made entirely of silica (silicon dioxide). These spicules are often six-rayed.
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