Which of the following animals exhibit metagenesis,similar to plants?

The characteristic feature of Phylum $Cnidaria$ is .....

Which of the following statement$(s)$ is/are correct regarding phylum $Coelenterata$ (Cnidaria)?
$(A)$ They are aquatic,mostly marine,sessile or free-swimming,radially symmetrical animals.
$(B)$ They have a central gastro-vascular cavity with a single opening on hypostome.
$(C)$ Digestion is extracellular and intracellular.
$(D)$ Their members are $Sycon$,$Spongilla$ and $Euspongia$.

Which of the following symmetry is found in adult sea-anemone?

In $Hydra$,the symmetry is

Coral is known as ........