A colonial algae among the following is :

Options

A. Chlamydomonas
B. Ulothrix
C. Volvox
D. Spirogyra

Answer

To solve the question "A colonial algae among the following is:", we need to analyze each of the given options to determine which one is classified as a colonial algae.

### Step-by-Step Solution:

1. **Understand the Definition of Colonial Algae**:
- Colonial algae are groups of algae that live together in a colony, often forming a structure that consists of multiple cells working together.

2. **Evaluate Each Option**:
- **Chlamydomonas**:
- This is a unicellular green algae that exists as individual cells. It is not colonial because it does not form groups or colonies.
- **Conclusion**: Not a colonial algae.

- **Eulothrix**:
- Eulothrix is a filamentous green algae. It consists of long chains of cells but does not form a colony in the sense of a cooperative group of cells.
- **Conclusion**: Not a colonial algae.

- **Volvox**:
- Volvox is a well-known example of colonial algae. It forms spherical colonies that can contain anywhere from 500 to 60,000 cells. These cells work together in a coordinated manner, making it a classic example of colonial algae.
- **Conclusion**: This is a colonial algae.

- **Spirogyra**:
- Spirogyra is also a filamentous green algae. It consists of long, unbranched filaments of cells and does not form colonies. The cells are arranged in a single line, and they do not cooperate as a colony.
- **Conclusion**: Not a colonial algae.

3. **Final Conclusion**:
- Among the options provided, **Volvox** is the only example of a colonial algae.

### Answer:
The correct answer is **Volvox**.