Answer: Option A
:
A
Many cnidarians exhibit metagenesis or alternation of generations. Obeliais a good example of this. The life history of Obelia includes both asexual and sexual generations that alternate with each other to complete the life cycle. The sedentary polyp is a colonial form, that alternates with the free-swimming medusa phase. The polyp colony reproduces by asexual budding. The medusa buds get detached from the parent colony, and become free-swimming sexual forms that carry ova and sperms in their respective gonads, and release them into the water. They then fertiliseto form a zygote, which later morphs into a blastula, then a ciliated swimming larva called a planula. The planula eventually attaches to a substrate and gradually develops into a polyp colony.