Explain Radial Symmetry in Classification of the Animal Kingdom?

All of the animals besides the sponges are considered to belong to the Eumetazoa, or the "true animals" because of several distinguishing characteristics. Unlike the sponges, eumetazoans possess a definite organization, or shape-their bodies have either radial symmetry or bilateral symmetry, and specialized tissues. Eumetazoan embryos all generate three distinct tissue layers that later form into the adult tissues and organs. These embryonic tissues include an outer tissue layer called the ectoderm, an inner endoderm, and a mesoderm layer that forms in the middle in between the ectoderm and the endoderm.