Which of the following cnidarian exhibits metagenesis?

Options

A. Hydra
B. Adamsia
C. Obelia
D. meandrina

Explanation

**Step-by-Step Solution:**

1. **Understanding Metagenesis**: Metagenesis refers to the alternation between two different forms in the life cycle of certain organisms, specifically the alternation between the medusa (free-swimming) and polyp (sessile) stages in cnidarians.

2. **Identifying the Options**: The options given are:
- A) Hydra
- B) Edentia
- C) Obelia
- D) Meandrina

3. **Analyzing Each Option**:
- **Hydra**: Hydra is a genus of small, fresh-water organisms that do not have a medusa stage. They only exist in the polyp form, which means they do not exhibit metagenesis. Therefore, this option is incorrect.

- **Edentia**: Edentia refers to sea anemones, which also do not have a medusa stage. They exist solely in the polyp form, thus they do not exhibit metagenesis. This option is also incorrect.

- **Obelia**: Obelia is a genus of colonial hydrozoans that exhibit both polyp and medusa stages in their life cycle. This alternation between the two forms indicates that Obelia does exhibit metagenesis. Therefore, this option is correct.

- **Meandrina**: Meandrina, known as brain coral, also lacks a medusa stage and exists only in the polyp form. Hence, this option is incorrect.

4. **Conclusion**: Based on the analysis, the only organism that exhibits metagenesis among the options provided is **Obelia**.

**Final Answer**: The cnidarian that exhibits metagenesis is **C) Obelia**.

---