Symmetry such that an organism is similar if divided in half along any plane. A common trait of organisms that are slow or non-motile and experience an environment that is fundamentally similar in every direction. On Old Earth and most other life-bearing planets most such organisms are microscopic, like radiolarians, since larger organisms experience a distinct up and down direction. However larger planktonic life forms in very deep atmospheres or oceans and some floating neogens in microgravity environments may show spherical symmetry. Compare with bilateral symmetry or radial symmetry.