While sponges and placozoans represent two groups of animals which do not show any symmetry (i.e. are asymmetrical), the body plans of most multicellular organisms exhibit, and are defined by, some form of symmetry. There are only a few types of symmetry which are possible in body plans. These are radial (cylindrical) symmetry, bilateral, biradial and spherical symmetry. While the classification of viruses as an "organism" remains controversial, viruses also contain icosahedral symmetry.