The bilateria /ˌbaɪləˈtɪəriə/ are the animals with bilateral symmetry, i.e., they have a front and a back end, as well as an upside and downside, and therefore a left and a right. In contrast, radially symmetrical animals like jellyfish have a topside and downside, but no front and back.The bilateria are a major group of animals, including the majority of phyla but not sponges, cnidarians, placozoans and ctenophores.