Polyp phase does not occur in

Options

A. Obelia
B. Aurelia
C. Hydra
D. Physalia.

Answer

To solve the question "Polyp phase does not occur in," we can follow these steps:

### Step 1: Understand the Polyp Phase
The polyp phase is one of the two main life forms in coelenterates (also known as cnidarians). The two forms are:
- **Polyp**: A sessile (non-moving) form that typically has a cylindrical body and is attached to a substrate.
- **Medusa**: A free-swimming form that is typically bell-shaped and can move through the water.

### Step 2: Identify the Organisms Listed
The options given in the question are:
1. Obelia
2. Aurelia
3. Hydra
4. Physalia

### Step 3: Classify Each Organism
- **Obelia**: Belongs to the class Hydrozoa, which has both polyp and medusa stages.
- **Aurelia**: Belongs to the class Scyphozoa, which primarily exhibits the medusa stage and does not have a polyp stage.
- **Hydra**: Also belongs to the class Hydrozoa and has both polyp and medusa stages, although it is primarily known for its polyp form.
- **Physalia**: Commonly known as the Portuguese man o' war, it is also part of Hydrozoa and has both stages.

### Step 4: Determine Which Organism Lacks the Polyp Phase
From the classification:
- **Aurelia** is the only organism that does not have a polyp phase, as it belongs to the class Scyphozoa, which is characterized by the medusa form.

### Conclusion
The correct answer to the question "Polyp phase does not occur in" is **Aurelia**.

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