Which of the following is not the function of cnidoblasts?

Through which structure does the coelenteron open at one end?

Which of the following phyla includes both freshwater and marine species?

Mesoglea is present between which of the following?

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 $Euspongia$.

Polymorphism is a characteristic feature of which of the following animal groups?