Category:Bilaterians

The bilateria /ˌbaɪləˈtɪəriə/ or bilaterians are animals with bilateral symmetry as an embryo, i.e. having a left and a right side that are mirror images of each other. This also means they have a head and a tail (anterior-posterior axis) as well as a back and a belly (ventral-dorsal axis).[2] Nearly all are bilaterally symmetrical as adults as well; the most notable exception is the echinoderms, which achieve near-radial symmetry as adults, but are bilaterally symmetrical during embryonic development.

Most animals are bilaterians, excluding sponges, ctenophores, placozoans and cnidarians. For the most part, bilateral embryos are triploblastic, having three germ layers: endoderm, mesoderm, and ectoderm.