Question

Metagenesis is characteristic to coelenterates, where tree
like polyps and umbrella like medusae are found in the life
cycle. Which coelenterate of the following exhibits this
phenomenon ?​

Answer 1

Answer:

Hydrozoa, Cnidarians exhibit two basic body forms called polyp and medusa. The former is a sessile and cylindrical form like Hydra, Adamsia, etc. whereas, the latter is umbrella-shaped and free - swimming like Aurelia or jellyfish. These Cnidarians, which exist in both forms exhibit alternation of generation (Metagenesis), i.e., polyps produce medusae asexually and medusae form the polyps sexually (e.g., Obelia).

Answer 2

Answer:

The answer is Obelia.

Explanation:

• Metagenesis (false alternation of generation) is a phenomenon in which one generation reproduces asexually followed by the next generation that reproduces sexually. This alternation of sexual and asexual reproduction keeps going in the life cycle of the generations.
• Example of a coelenterate that shows metagenesis is Obelia. It has two stages, the polyp (tree-like), and the medusae (umbrella-like).
• Obelia - It belongs to the phylum Cnidaria and class Hydrozoa. It is a tiny marine hydroid invertebrate. It has radial symmetry and is brilliantly colored. It has a gastrovascular cavity and tentacles (extensions of the body wall). It shows alternation of generation between the Polyp reproductive stage and the Medusae reproductive stage.
• The Polyp Reproductive Stage - It is the first stage of the obelia. It reproduces asexually. It is immobile, and remain attaches to a solid surface such as the ocean floor. It has stalks and tentacles. These are called sea furs because their structures resemble sea anemones. It gives rise to the free-swimming medusae after budding.
• The Medusae reproductive Stage - It is bell shape and has tentacles. It resembles jellyfish. It is free-swimming. It reproduces sexually. It gives rise to the free-swimming larvae after fertilization. These larvae reach the ocean floor, get attached, and give rise to the polyp stage.

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