Mammalian erythrocytes are

Options

A. Circular
B. Biconcave
C. Non-nucleated
D. All the above .

Answer

### Step-by-Step Text Solution:

1. **Definition of Mammalian Erythrocytes**:
- Mammalian erythrocytes refer to red blood cells (RBCs) found in mammals. Their primary function is to transport oxygen throughout the body.

2. **Shape of Erythrocytes**:
- Erythrocytes are typically circular in shape. However, they exhibit a biconcave structure, which enhances their surface area for oxygen absorption and allows them to deform as they pass through narrow capillaries.

3. **Nucleus in Erythrocytes**:
- Unlike many other cells, mammalian erythrocytes are non-nucleated. The absence of a nucleus is crucial because it allows more space for hemoglobin, the protein that binds oxygen. If a nucleus were present, it would consume some of the oxygen transported.

4. **Conclusion**:
- Based on the characteristics discussed, mammalian erythrocytes are circular, biconcave in shape, and non-nucleated. Therefore, the correct answer to the question about mammalian erythrocytes is "all of the above."