The arrangement of parts in an organ or organism such that cutting through the centre of the structure in any direction produces two halves that are mirror images of each other. The stems and roots of plants usually show radial symmetry, while all animals belonging to the Cnidaria (e.g. jellyfish) and Echinodermata (e.g. starfish) are radially symmetrical—and typically sessile—in their adult form. The term actinomorphy is used to describe radial symmetry in flowers (e.g. a buttercup flower). Compare bilateral symmetry.