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Cnidarians or coelenterates are a part of the animal kingdom. Surprisingly, this phylum contains around 9000 species in it; it is majorly dominated by primitive aquatic animals like a hydra, jellies, corals, sea anemones, etc. This phylum is further divided into four classes which are- Hydrozoa, Scyphozoa, Anthozoa and cubozoa.
The characteristics of this phylum are astonishing, and the niche they create in the aquatic habitat is also mesmerising. But another astonishing feature is that their life cycle is divided into two stages- polyps and medusa.
Polyps and Medusa
Cnidarians are divided into polyps and medusa based on their life stage and complexity of body organisation. Polyps can be called the less evolved and the basic coelenterates, whereas medusa can be called the complex and organised body.
Cnidarians divided into polyps and medusa
In some cnidarians, these two life stages- polyps and medusa alternate one by one in hydrozoans, whereas jellyfish only exist in the complex medusa form.
While other members of the hydra division exhibit polyp form.
Description of Polyps
- Polyps are immobile. That is, they cannot locomote
- Polyps have mouths that are outlined by tentacles. These together form the head of the organism, which is connected to the bottom and has a broader base. The mouth faces towards the water
- Polyps can reproduce in both ways- sexually and asexually
- Corals are bisexuals and sometimes hermaphrodites, whereas asexual reproduction occurs through budding
- Some of the famous polyps are adult corals and sea anemones
Description of medusa
- Medusa are organisms that can locomote in the water. For example, they can swim through muscle contraction. These are shaped like a bell. The surface of this bell-like structure has tentacles, which are very specific for specific stimuli, for example- photoreceptors, statocytes, etc.
- Their characteristic feature is the presence of a manubrium, a tube-like structure protruding from the inside of a bell-like structure; this manubrium acts like a mouth
- Medusa reproduces sexually and can also be developed from hydrozoa by the metamorphosis of polyps (polyps that reproduce sexually through spawning)
Major differences between polyps and medusa
Conclusion
Polyps and medusae are the life stages of the organisms from the phylum cnidaria or coelenterates. Both have specific characteristics morphologically and physiologically attached to them. Polyps are very primitive with very low organisation, whereas medusa is complex. There are differences in morphology and physiology.
