Tell some fundamental features which are used as the basis of animal classification.

Explanation

To answer the question about the fundamental features used as the basis of animal classification, we can outline the following steps:

### Step-by-Step Solution:

1. **Level of Organization**:
- Animals are classified based on their level of organization. This can range from simple cellular organization in unicellular organisms to complex tissue and organ systems in multicellular organisms.

2. **Body Symmetry**:
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