Difference Between Polyp and Medusa

Polyp and Medusa are two different body forms, here one is nonmotile in nature and other is in free swimming. These two structures are found in invertebrates phylum Cnidaria i.e Coelenterates. Some of them exist in polyp form while others are in  medusa form as these forms are staged in their life. Some species of Cnidaria have both stages i.e polyp and medusa, example: Hydrozoa. Some other examples of cnidarians are corals, sea anemones, jellyfish, hydroids, etc.

Polyp:

Polyp is a sessile life cycle stage of species who belong to phylum cnidaria. Famous examples of polyp are sea anemones and adult corals. Polyp is formed with a mouth surrounded with tentacles, referred to as a head and head is attached to the bottom with a foot-like disk. Direction of the mouth and tentacles face towards the water. Mode of reproduction in polyp is either sexual or asexual. Corals have separate sexes, some corals have male organs while others have female organs in the same ways some of the corals are hermaphrodites in nature i.e they have both male and female organs on the same body. Here mode of asexual reproduction is budding i.e through formation of buds that form new individuals and sexual reproduction occur by spawning. At a given time following the secretion of pheromones, corals release a big number of sexual cells in the water.

Medusa: 

Medusa is a life cycle stage of the species who belongs to cnidaria phylum. One of the most common examples of species having a medusa life cycle is Hydrozoa or jellyfish. External appearance of medusa is bell shaped and has capability of undergoing muscular contractions which enables the medusa to swim. Several types of tentacles like photoreceptors, gravity-sensing osteocytes surround the bell. Members of the Hydrozoa class specially possess manubrium, whose structure is like a tube hanging down from the bell with the mouth at its end. Mode of reproduction in medusa is sexual, but their development varies within the class of the cnidaria phylum as in case of hydrozoa class new members are formed by budding. While in other cnidarian classes such as cubozoa or rhizostomeae medusa are produced by the metamorphosis of the polyp. 

Difference between Polyp and Medusa: 

There are many difference seen in polyp and medusa based on their external as well as internal features: 

1. Movement of Polyp and Medusa: 

Polyp is a sessile life stage of the cnidaria phylum whereas medusa is totally opposite i.e they have a mobile life cycle stage of the cnidaria phylum. 

2. Morphology of Polyp and Medusa:

Morphological features of polyp are tubular in shape and they are fixed at their base. Their mouth is present at the opposite end and is surrounded with tentacles forming the head part. Their month and tentacles face the direction of water. Whereas medusa have the shape of a muscular bell which enables them to swim. In the case of Hydrozoa, their mouth is present at the end of a tube hanging down from the bell, which is known as manubrium. Several external structures like tentacles, photoreceptors, gravity-sensing osteocytes surround the bell. Among these external receptor photoreceptors and statocytes act as a sense organs present only in medusa and lacking in the polyp. 

3. Reproductive Ability of Polyp and Medusa:

Reproductive ability of poly is asexual mode i.e by budding through evagination of a circular are of tissue including the endosperm and ectoderm, or they also reproduce sexually by spawning following the release of pheromones. Some of the polyps exist in hermaphrodite form. Budding in polyp can form either polyp or medusa. Whereas medusa reproduce sexually only and they give rise to medusa live stage cycle only.

4. Evolution Happened in Polyp and Medusa:

Medusa is the evolved form of poly as poly is the primitive form of life stage in cnidaria phylum. There is a large diverse feature between polyp and medusa which are evolved by passage of time, some of these features are medusa sexual reproductive ability, medusa free swimming ability as all these features are complex morphological features than that of polyp, as polyp lacks all these features. Presence of a photoreceptor is also an evolved feature of polyp.

Comparison between Polyp and Medusa:

Many species of the phylum Cnidaria have two separate life cycle stages: polyp and medusa. The phylum Cnidaria contains species that only exist in the polyp stage (Anthozoa), species that only exist in the medusa stage (Cnidaria), and species that occur in both life cycle stages (Cnidaria) (Hydrozoa).

Cnidarians include corals, sea anemones, jellyfish, and hydroids. 

Polyp

• A polyp is a sessile life cycle stage in the Cnidaria phylum of organisms. Polyps are seen in adult corals and sea anemones.

• A polyp is made up of a tube with a mouth surrounded by tentacles. It is called a "head,". It also has a foot-like disc that is attached to the bottom of the tube. The mouth and tentacles are pointing in the direction of the water.

• Polyps can reproduce either sexually or asexually. Separate sexes exist in corals, with some corals being males and others females, while other coral species are hermaphrodites, with one individual being both male and female.

• Budding happens when a circular area of tissue, comprising the endoderm and ectoderm, is evaginated during asexual reproduction.

• Sexual reproduction takes place by Spawning. Corals discharge a large number of sexual cells into the water after secreting pheromones at a specific moment.

Medusa

• Medusa is a species' mobile life cycle stage in the Cnidaria phylum.

• Hydrozoa species can take the form of a medusa or a jellyfish.

• A medusa is formed morphologically by a bell capable of muscular contractions, allowing the medusa to swim.

• There are tentacles with a different shape than polyps, photoreceptors, and gravity-detecting osteocytes that surround the bell.

• Hydrozoa members also have a manubrium, which is a tube that hangs down from the bell and has a mouth at one end.

• The gastric cavity is defined as the space between the manubrium's base and the bell. Medusa procreates sexually.

• Medusa development differs among the Cnidaria phylum's classes. Medusa is created through budding Hydrozoa class members. Following the evagination of the endoderm and ectoderm, ectodermal epithelial cells proliferate near the bud's tip, generating an interior cavity.

• The cavity then opens, tentacles grow, and the tissue that connects the medusa to the parent polyp constricts, allowing the freshly born medusa to emerge.

• Medusa is created by the transformation of the polyp in other cnidarian classes, such as Cubozoa or Rhizostomae.

Polyp and Medusa: Major Differences