What is metagenesis? Mention an example which exhibits this phenomenon.

(N/A) Metagenesis is the phenomenon of alternation of generation in certain cnidarians,where the asexual polyp form alternates with the sexual medusa form in the life cycle.
In this process,polyps produce medusae asexually,and medusae produce polyps sexually.
An example of an organism that exhibits metagenesis is $Obelia$.