Hydra has

Where are cnidoblasts found?

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 $Euspongia$.

Metagenesis is observed in the context of ............... .

Select the taxon mentioned that represents both marine and fresh water species.

In $Hydra$,waste materials after digestion and nitrogenous waste materials are removed from