These are two types of body forms identified in the Cnidarians. They are the life cycle stages of many species. The phylum Cnidaria consist of species that exist only in the polyp stage, those that exist in the medusa stage, and those that exist in both the stages,
The main difference between polyp and medusa is that polyp is a fixed, cylindrical structure representing the asexual stage while medusa is a free-swimming, umbrella-like structure representing the sexual stage.
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Comparison Table (Polyp vs Medusa)
| Characteristics | Polyp | Medusa |
| Body structure | Cylindrical structure containing a long stalk. | Saucer-shaped, an umbrella-like structure containing reduced stalk. |
| Movement | It is a sessile organism. | It is a free-swimming organism. |
| Habitat | It is found attached to the rocks near watermarks. | It is found in open waters. |
| Manubrium | The manubrium is directly upward since the body is attached to the surface. | It hangs downwards since the base is above. |
| Velum | It does not have velum. | It has a velum. |
| Sense organs | It does not have a sense organ. | Statocysts are present at the base of eight adradial tentacles. |
| Gastrovascular cavity | Simple and lacks radial and circular canals.
|
It is the stomach and comprises four radial and circular canals. |
| Gonads | It does not have gonads. | It consists of four gonads. |
| Reproduction | It reproduces asexually by budding. | It reproduces sexually by gametes. |
| Role | It is concerned with feeding, protection, and asexual reproduction. | It is concerned with sexual reproduction. |
| Evolution | They are primitive forms of Cnidaria. | They are the more evolved form of Cnidaria. |
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What is Polyp?
A polyp is a sessile life stage of the species belonging to the Cnidaria phylum. Examples of polyps include adult corals and sea anemones. They are cylindrical-shaped animals. They are attached to the substrate by their adoral ends. Some polyps form colonies and each colony is attached to the other either directly or indirectly.
Their mouth is found at the oral end and it is surrounded by tentacles. They reproduce asexually by budding. The wall of the polyps comprises two cell layers. The outer layer is called the ectoderm while the inner layer is the endoderm.
Their stomach is enclosed by the endoderm. The polyps are simple animals considered as fossils that have no change for about half a billion years.
What is Medusa?
Medusa is a mobile life cycle stage of the species belonging to the phylum Cnidaria. Medusa is formed by a bell capable of muscular contractions which enables the medusa to swim. The bell is surrounded by tentacles.
Tentacles are either used to capture prey or defend themselves from predators. They contain toxins in a painful sting. At the base of the bell, there is a mouth or anus. Jellyfish is considered the oldest multi-organ animal.
They have a loose network of nerves called nerve-net located in the epidermis. Some jellyfish have light-sensitive organs called ocelli. Medusa releases sperms or eggs into the surrounding water during their sexual reproduction then the fertilized eggs mature into new organisms.
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Main Differences between Polyp and Medusa
- A polyp is a sessile organism while a medusa is a free-swimming organism.
- A polyp is a cylindrical structure with a long stalk while a medusa is an umbrella-shaped structure with a reduced stalk.
- Polyps are found attached to the rocks near watermarks while medusa is found in open waters.
- Polyps are a primitive form of Cnidaria while medusa is the more evolved form of Cnidaria.
- Polyps do not have velum while medusa has velum.
- Polyps do not have gonads while medusa has four gonads.
- Polyps do not have a sense organ while medusa has a statocyst at the base of eight adradial tentacles.
- Polyps reproduce asexually by budding while medusa reproduces sexually by gametes.
Similarities between Polyp and Medusa
- They are both from the phylum Cnidaria.
- They are both life cycle stages of different organisms.
- They both have tentacles.
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In Conclusion
Both polyps and medusa are life stages of different organisms. Polyps are sessile and they reproduce asexually by budding while medusa is free-swimming organisms and reproduce sexually by gametes. The main features that make polyps different from medusa are; reproduction and movement methods.
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