Triploblasty

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Triploblasty is a condition of the blastula in which there are three primary germ layers: the ectoderm, mesoderm, and endoderm. Additionally, the term may refer to any ovum in which the blastoderm splits into three layers. All higher and intermediate animals (from flat worms to humans), arise from a triploblastic ovum. Triploblastic organisms are organisms which evolve from such an ovum. Generally speaking, triploblastic organisms belong to the Bilateria subregnum. Compare to simpler diploblastic animals such as cnidaria with two germ layers and even simpler animals such as sponges with only one germ layer.