Which phylum consists of animals that exhibit radial symmetry?

In which phylum are nerve cells found but nerves are absent?

Which statement is correct regarding the nematocyst in $Hydra$?

Which of the following cells are present only in the epidermis of Hydra?
$(A)$ Interstitial cells
$(B)$ Cnidoblasts
$(C)$ Sensory cells
$(D)$ Germ cells

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

Blind sac body plan is shown by