Evolutionary Challenges Plants and animals have adopted very different strategies to solve these problems. And different groups of animals have come up with some solutions that are truly radical. The possible solutions, however, are not infinite. Any engineer can tell you that the number of solutions to an engineering problem is finite. The basic laws of physics and chemistry are not repealed when we put up a building.
Radial symmetry means the animal can be folded along any plan into mirror image halves.
Like a wagon wheel. Bilateral symmetry means that there is only one plane that can divide the organism into mirrored halves, like a wagon. The Phylum Cnidaria is a large group of organisms that are sessile for all or part of their existence. Sea anenomes, for example, or coral polyps live out their lives attached to the same spot. Radial symmetry in these organisms is probably a fundament adaptation to a sessile existence.