For example, in neurogenesis, a subpopulation of ectoderm cells is set aside to become the brain, spinal cord, and peripheral nerves.
en.wikipedia.org It is not a teratoma, however, which is a neoplasm comprising all three germ cell layers (ectoderm, endoderm, mesoderm).
en.wikipedia.org In triploblastic organisms, the three germ layers are called endoderm, ectoderm, and mesoderm.
en.wikipedia.org All the more complex animals (from flat worms to humans) are triploblastic with three germ layers (a mesoderm as well as ectoderm and endoderm).
en.wikipedia.org Animals with radial symmetry, like cnidarians, produce two germ layers (the ectoderm and endoderm) making them diploblastic.
en.wikipedia.org