Which organism is called living fossil?

Explanation

**Step-by-Step Solution:**

1. **Understanding the Term "Living Fossil":**
- A living fossil refers to an organism that has remained relatively unchanged over millions of years. These organisms retain primitive characteristics that were present in their ancestors.

2. **Characteristics of Living Fossils:**
- Living fossils exhibit very low variation in their physical traits compared to their ancient relatives. They possess simple and old features that have persisted through time.

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