Each rotor is radially symmetrical, but laterally asymmetric. They are radially or (rarely) laterally symmetric, and generally hermaphroditic. They consist of a cylinder or disk with teeth projecting radially. Because of their shape, paraboloid domes experience only compression, both radially and horizontally. They are bilaterally or radially symmetrical. The histologic pattern consists of nesting of squamous epithelium bordered by radially arranged cells. Brakes consisted of radially vented brake discs front and rear. In the zona fasciculata, cells are arranged in columns radially oriented towards the medulla. Each of the radially symmetrical, star-shaped flowers has six petals. The flowers are almost always radially symmetrical. Bilaterians likely evolved from an ancestor which was radially symmetrical. These include flowers that are usually radially symmetric and petals that are free. They are actinomorphic (i.e. radially symmetrical) and almost always hermaphroditic. The scolex bears four radially arranged suckers that surround the rostellum. Six radially arranged stairs divided the lower part of the koilon in seven tiers.