Concept:Radial symmetry means the body can be divided into equal halves along multiple planes around a central axis.
Explanation:Organisms with radial symmetry have no distinct left or right side, and no clear head or tail.
This symmetry is common in simple, often sessile or slow-moving aquatic animals.
Cnidarians, such as Hydra, jellyfish, and sea anemones, show radial symmetry.
Planaria, tapeworms, and roundworms all display bilateral symmetry, with distinct head and tail regions.
Therefore, among the options, Hydra is the radially symmetrical organism.
Answer:B. Hydra