"The bilateria /ˌbaɪləˈtɪəriə/, bilaterians, or triploblasts, are animals with bilateral symmetry, i.e., they have a head (anterior) and a tail (posterior) as well as a back (dorsal) and a belly (ventral); therefore they also have a left side and a right side.
The bilateria are a major group of animals, including the majority of phyla but not sponges, ctenophores, placozoans, and cnidarians. For the most part, bilateral embryos are triploblastic, having three germ layers: endoderm, mesoderm, and ectoderm. Nearly all are bilaterally symmetrical, or approximately so; the most notable exception is the echinoderms, which achieve near-radial symmetry as adults, but are bilaterally symmetrical as larvae." - (en.wikipedia.org 24.09.2019)
en