( by-leh- teer-ee-uh) [L. bi, twice, two + lateris, side] Members of the branch of eumetazoans possessing bilateral symmetry.

The Bilateria, having bilateral symmetry, are a subregnum (a major group) of animals, including the majority of phyla; the most notable exceptions are the sponges and cnidarians. For the most part, Bilateria have bodies that develop from three different germ layers, called the endoderm, mesoderm, and ectoderm. From this they are called triploblastic.