The first cell layers that appear in the development of all animals, and from which the embryo body and extraembryonic membranes (when present) are constructed. The cells of the early embryo (the blastula) are organized into supracellular units, the germ layers. These are more or less distinct anatomically but do not necessarily have sharp boundaries of demarcation, in part because one layer gives rise to another. Germ layers are universal among animal embryos; they are an efficient method for establishing discontinuities of architectural importance and for setting aside what will become lineages of cells with different fates.