Many members of the phylum Cnidaria have two distinct steps in the process: a polyp formation and a medusa. The division Cnidaria contains species that only occur in the polyp phase aka anthozoans, species that only occur in the medusa stage Cnidarians, and species that occur across both life cycle phases are Cnidaria Hydrozoans.
Well, this article only concentrates on pointing out the distinct features and differences between the two phases i.e. polyp phase and medusa phase of the Cnidaria phylum. Also, this article highlights the differences in the form of comparison tables and important pointers to clear out every doubt that has brought you to this article.
Polyp vs Medusa
The difference between polyp and medusa is that the ability to locomote, polyps are stagnant animals with no ability to freely swim whereas medusae class organisms can freely swim in the seawater. Now, both the forms are Cnidarian aspects, and thus the basic life processes are similar however, the polyps usually have a long stalk attached to the center of their body like the Hydra is a good example whereas the coelom or cavity is found in the medusae members like the flat or box jellyfishes.
In biology, a polyp is one of 2 key body shapes seen in inhabitants of the Cnidarian animal kingdom. The polyp is solitary and sessile and can be isolated, as in a sea anemone, or a coral. They usually are stalked to a place and no movement occurs in them. The mouth is usually encircled by extendable tendrils that carry sophisticated stinging mechanisms called nematocysts on the top, and free, end of the body, which is empty and tubular. Prey is captured by the tentacles and pulled into the so-called mouth.
Medusa, on the other hand, is the second body form obtained by the Cnidarians. Looking carefully, it is significantly a good example to consider box jellyfish’s common form. The umbrella-like and drooping structure of a medusoid is its key appearance indicator. The manubrium, a vine feature with the mouth at its apex, hangs downwards from the middle. The mouth opens into the main section chamber or the enteron (where the food enters) which is connected to radial tubes that continue to the bell’s periphery.
Comparison Table Between Polyp and Medusa
|Parameters of Comparison||Polyp||Medusa|
|Locomotion||Polyps are sessile animals which cannot swim and usually stay attached to the same place forever.||Members of medusae can swim freely in open water.|
|Sensory Organs||No sensory organs are present and nervosa ring is absent as well.||Statocysts are present and the sensory part is adradial tentacles which are usually 8 in number.|
|Reproduction Phase||Reproduces asexually (budding) or sexually and gives birth to either a polyp or a medusa.||Reproduces to give birth to a medusa only. Mode is sexual and using gametes.|
|Body Shape||Cylindrical and tubular structure||Saucer-like and usually looks like an umbrella.|
|Examples||Sea anemones, sea fans, coral and sea pens.||Jellyfishes, mawsonites, rhizostomeae etc.|
What is Polyp?
A polyp is a motile lifespan phase within the Cnidarian phylum of creatures. Polyps are seen in adult reefs and sea urchins. A polyp is made up of a tube with an opening encircled by tendrils, referred to as a “head,” and a foot-like disc connected to the base. The opening and tendrils are pointing in the direction of the ocean water flow to trap the planktons for food.
Polyps can reproduce either asexually (by budding) and sexually (corals are gender-based organisms). Different sexes occur in corals, with maybe some corals becoming males and others females. Some species of corals are hermaphrodites and the gender depends upon the temperature of the water they reside in. Budding happens when a spherical area of tissue is evaginated during asexual reproduction.
Speaking about their body structure, Polyps are cylindrical in form and have a fixated shaft-like base. The opening or the upper mouth of the creature is at the opposite end of the cylinder, encircled by tentacles that create the “head.” The mouth and tendrils are pointing towards the water.
Individuals in a swarm of invertebrate sea organisms belonging to the group Bryozoa are occasionally referred to as polyps, although they are typically referred to as zooids the name for these phyla (polyp) is derived from zooids themselves.
What is Medusa?
Medusa is a Cnidaria phylum organism’s movable life cycle phase. Hydrozoa taxa can take the form of medusas or jellies. A medusa is anatomically created by a bell susceptible to muscular activity, allowing it to move and swim. The dome-like structure is surrounded by tendrils with a distinct morphology than polyps, photoreceptor cells, and osteocytes. Hydrozoa species also have a manubrium, which is a cylinder that hangs from the ring and has a hole at the bottom.
The mouth is on the bottom part, which may be half-closed by a cellular structure spanning inward from the edge known as the vellum. The top or aboral exterior has named the exumbrella (which looks like the exterior of an umbrella), and the bottom part is called the subumbrella.
The gastrovascular chamber and projecting tubes that stretch forward towards the edge make up the gastrointestinal cavity; these channels can be basic or branched, and their quantity can range from a few to a lot. Sensory organs and tendrils are found along the disk’s edge.
The medusa is an independent swimming creature that propels itself across the water via repetitive muscle contractions of the umbrella structure. Scyphozoa (the popular, multicolored, big jellies like the box jellyfish) and Cubozoa are the most frequent medusa species. Because those are the only groups in which medusae may be found, except for aquatic hydrozoans.
Main Differences Between Polyp and Medusa
- Polyps cannot move or locomote whereas medusae can swim.
- Polyps are cylindrical and clustered in structure whereas medusae are bell-like in appearance.
- Polyps do not have sensory organs whereas medusae have sensory organs and tendrils.
- Polyps have a simpler gastrointestinal system whereas medusae have a complex digestive system.
- Polyps can reproduce sexually as well as asexually whereas medusae can only reproduce sexually by gametes.
The Cnidaria phylum has two lifespan phases: polyp and medusa, which alternate in certain taxa, whereas other Cnidaria organisms exist either as a polyp in the Anthozoa category or medusa in the Hydrozoa category.
Polyps are immobile and reproduce both sexually and asexually through budding and gamete transfer depending upon the coral breed. Medusa, on the other hand, replicates sexually, generating embryos. The main distinction between polyp and medusa is that the former is solitary and immobile and the latter is free-swimming.