An animal body plan that is triploblastic and coelomate has three main layers of tissue during development.
The germ layers are tissue layers which develop early in embryonic life, through the process of gastrulation. During gastrulation, a hollow cluster of cells-blastula reorganizes into two primary germ layers: an inner layer- endoderm, and an outer layer, - ectoderm which interact to produce a third germ layer - mesoderm. Together, the three germ layers will give rise to every organ in the body. For example, ectoderm will form skin, endoderm will form digestive tract and mesoderm will be involved in the formation of visceral organs like the stomach.