Polyp vs. Medusa

Main Difference

The main difference between the polyp and Medusa is that polyp is a cylindrical, fixed and presenting an asexual stage on the other side medusa is an umbrella-like structure, free swimming and representing the sexual stage.

Difference Between Polyp and Medusa

Comparison Chart

Polyp vs. Medusa

A polyp is a fixed and sessile organism present in water body while Medusa is free living and free swimming animal found in oceans and seas. Polyps are attached to the rocks, and its substrates as they are fixed on the other hand medusae are found in open oceans as they can move quickly. Polyps have no sense organs while medusa has sense organs which are present on their tentacles. Polyp’s body is cylindrical in shape and has a long stalk whereas the medusa’s body is umbrella-like or saucer-shaped and having a reduced stalk. Velum is not present in polyps while velum is present in Medusa. Polyps are concerned with the protection, feeding and asexual reproduction on the other side medusa are concerned with sexual reproduction. Polyps reproduce by asexual reproduction by forming the buds while medusa reproduces by sexual reproduction by gametes. Polyps have a long stalk in their body structure whereas the Medusa has a short and reduced stalk in their body structure. Polyps lack the gonads whereas medusa has four gonads on radial canals. Polyps have a simple gastrovascular cavity by having no radial or circular canals while Medusa has the gastrovascular cavity showing the stomach and radial canals. In polyps, the body is attached to the below, so the manubrium is present directly upward while in medusa body is above so the manubrium hangs downward.

What is Polyp?

A polyp is one of the two body forms which are found in Cnidarians. They are a cylindrical-shaped organism. Polyps are attached to the substrate or rocks by their adoral end. This type of attachment occurs via the pedal disc which is a disk-like holdfast. Some polyps live in colonies. In the colony, each polyp is connected to the other polyps either directly or indirectly. The mouth of polyps is present at the oral end, and their mouth is surrounded by a circle of tentacles. Polyps reproduce asexually by the process of budding.

The body of polyps can be considered as a sac. The wall of the polyp is made of two layers of cells. The outer layer is technically known as the ectoderm, and the inner layer is called the endoderm. The endodermis is also known as the gastroderm as the stomach is enclosed by the endoderm layer. A supporting layer also presents between the ectoderm and the endoderm. The supporting layer is known as the mesoglea which is made of a gelatinous substance which has no specific structure and secreted by the layers of cells of the body wall. The mesoglea also vary from the fragile layer to a fair thickness. Sometimes it consists of skeletal elements which are formed by the cells migrated to form the ectoderm. As the class Anthozoa is fixed or sessile, they always comprised of polyps. Class Hydrozoa consists of Hydra, like a polyp. In the Class Scyphozoans, larval planula metamorphoses is a polyp. This polyp is also known as the scyphistoma.

What is Medusa?

Medusa is also the body form which is found in Cnidarians. Medusae are aquatic or water requiring animals which are called as free-swimming and free-living soft bodies. Medusa contains an umbrella-shaped bell that is gelatinous material along with the trailing tentacles. The bell palpitates to obtain the propulsion and locomotion. Tentacles are also used to capture the prey and also used to defend against the predators as the tentacles contain toxins which are present in a painful sting.

The mouth and anus both are located at the base of that bell. Jellyfish are known as the oldest multi-organ, medusian animal as jellyfish are found in oceans, and present at the surface of ocean as well as in the deep seabed. Jellyfish roamed the ocean or sea at least 500 million years. They also have a loose network of nerves which is considered as the nerve net which is located in the epidermis. Some jellyfishes also have light-sensitive organs which are known as the ocelli.

In class Hydrozoa, Siphonophores are the medusian animals. In class Scyphozoa medusa stage is dominant. In the planula of the Scyphozoans, scyphistoma is developed into another stalk of plate-like Medusa. From the larval planula stage, swimming away and pinching off in this medusa form is called strobilation. The life cycle of Cubozoans also takes place in Medusa. During the sexual reproduction, medusa release sperms and eggs into the nearby water. The fertilized egg becomes mature and forms the new organism.

Conclusion

Conclusion of this article is that both polyp and medusa belong to class Cnidarian. The only difference is that polyp is sessile representing the asexual method while Medusa is free-living and representing sexual reproduction.