bilateria

The Bilateria are those animals which have a body composed of three different germ layers, called the endoderm, mesoderm, and ectoderm. These animals are also called triploblastic.

The Bilateria include all animals that are (more or less) bilaterally symmetrical and, except for a few flatworms, have an internal body cavity (coelom or pseudocoelom) with a mouth at one end and an anus at the other. The Bilateria include the majority of animals, with the cnidarians and sponges being the principal exceptions.