Which coral species is extensively used in jewellery?

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 $Euspongia$.

Testes are located in $Hydra$ at:

Describe the location and function of the following structures in Phylum Coelenterata:
$(i)$ Tentacles
$(ii)$ Hypostome

Through which structure does the coelenteron open at one end?

Sea anemone belongs to which class?