Find the odd one among the following taxa w.r.t presence of double circulation.

Options

A. Pisces
B. Aves
C. Reptiles
D. Mammalia

Answer

To find the odd one among the following taxa with respect to the presence of double circulation, we need to analyze each group mentioned: Pisces (fish), apes, reptiles, and mammals.

### Step-by-Step Solution:

1. **Understanding Double Circulation**:
- Double circulation refers to the process where blood passes through the heart twice during one complete circuit of the body. This includes the pulmonary circuit (to the lungs) and the systemic circuit (to the rest of the body).

2. **Identifying the Circulatory System in Each Taxon**:
- **Pisces (Fish)**: Fish have a single circulatory system. Blood is pumped from the heart to the gills for oxygenation and then directly to the body. This is not double circulation.
- **Apes**: Apes, being mammals, have a double circulatory system. They have a four-chambered heart that separates oxygenated and deoxygenated blood completely.
- **Reptiles**: Most reptiles have a three-chambered heart (two atria and one ventricle), which leads to some mixing of oxygenated and deoxygenated blood. They exhibit incomplete double circulation.
- **Mammals**: Like apes, mammals have a four-chambered heart, ensuring complete separation of blood and thus double circulation.

3. **Conclusion**:
- Among the taxa listed, **Pisces (fish)** is the odd one out because they do not have double circulation; they have a single circulatory system. Reptiles have an incomplete double circulation, while apes and mammals have complete double circulation.

### Final Answer:
**Pisces (fish)** is the odd one out with respect to the presence of double circulation.