Polyp and medusa are the two primary body forms found in animals belonging to the phylum Cnidaria. According to the provided reference, they represent distinct morphological adaptations within this group.
Understanding Polyp and Medusa Forms
| Feature | Polyp | Medusa |
|---|---|---|
| Mobility | Non-motile (sessile) | Free-swimming |
| Shape | Cylindrical with a long stalk | Umbrella-shaped |
| Stalk | Present and prominent | Reduced or absent |
| Examples | Hydra, coral polyps | Jellyfish |
| Orientation | Mouth and tentacles usually facing upwards | Mouth and tentacles usually facing downwards |
Polyp Form Explained
The polyp is a sessile, or non-motile, form. Key characteristics include:
- Cylindrical Shape: The body is generally tube-shaped.
- Attachment: It attaches to a surface via a stalk.
- Example: Hydra is a classic example of an organism existing in the polyp form. Coral polyps are also a good example.
Medusa Form Explained
The medusa is a free-swimming form. Its key features are:
- Umbrella Shape: The body resembles an umbrella or bell.
- Motility: It moves freely through the water.
- Example: Jellyfish are the most recognizable example of the medusa form.
Many cnidarians exhibit both polyp and medusa forms during their life cycle (alternation of generations), while others exist solely as either a polyp or a medusa. This adaptability allows cnidarians to occupy a wide range of marine and freshwater habitats.
