An aquatic living fossil, with ancient origin and many primitive characters which respires through book lungs is

Options

A. Limulus
B. Cancer
C. Lucifer
D. Daphnia.

Answer

To solve the question, we need to identify the aquatic living fossil that has ancient origins, possesses many primitive characteristics, and respires through book lungs. Let's break down the options provided:

1. **Daphnia**: This is a genus of small crustaceans commonly known as water fleas. They respire through diffusion and are not considered living fossils.

2. **Lucifer**: This is a genus of small shrimp-like crustaceans. They respire through gills, which disqualifies them from being the answer.

3. **Cancer**: This refers to a genus of crabs. Like Lucifer, they also respire through gills, so they do not fit the criteria.

4. **Limulus**: This is the genus of horseshoe crabs, specifically Limulus polyphemus, also known as the American Horseshoe Crab. Horseshoe crabs are considered living fossils due to their ancient lineage and many primitive characteristics. They respire through book gills, which are similar to book lungs.

Based on this analysis, the correct answer is **Limulus**.

### Step-by-Step Solution:
1. **Identify the characteristics needed**: Look for an aquatic living fossil with ancient origins, primitive traits, and respiration through book lungs.
2. **Evaluate each option**:
- Daphnia: Respiration through diffusion, not a living fossil.
- Lucifer: Respiration through gills, not a living fossil.
- Cancer: Respiration through gills, not a living fossil.
- Limulus: Known as horseshoe crab, has ancient origins, primitive features, and uses book gills for respiration.
3. **Conclude the answer**: The only option that meets all criteria is Limulus.