The alternation of Polyp and medusa forms in coelenterates is called as:

Answer

To solve the question regarding the alternation of polyp and medusa forms in coelenterates, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Identify the Forms**: Understand that coelenterates (also known as cnidarians) have two main forms: the polyp and the medusa.
- **Polyp**: This is the sessile (stationary) form, typically cylindrical in shape, and often attached to a substrate.
- **Medusa**: This is the free-swimming form, typically umbrella-shaped, and is capable of moving through the water.

2. **Understand the Reproductive Processes**: Recognize how these two forms reproduce:
- **Polyp Reproduction**: The polyp can reproduce asexually, often by budding, to produce medusa.
- **Medusa Reproduction**: The medusa reproduces sexually, releasing gametes (sperm and eggs) into the water, which then develop into polyps.

3. **Define the Concept of Alternation of Generations**: The process where two different forms (polyp and medusa) alternate in the life cycle of an organism is known as alternation of generations.

4. **Identify the Specific Term**: In the case of cnidarians, this specific alternation between the polyp and medusa forms is referred to as **metagenesis**.

5. **Conclusion**: Therefore, the answer to the question is that the alternation of polyp and medusa forms in coelenterates is called **metagenesis**.

### Final Answer:
The alternation of polyp and medusa forms in coelenterates is called **metagenesis**.

---