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Triploblasty is a condition of the blastula in which there are three primary germ layers: the ectoderm, mesoderm, and endoderm. A fourth "layer" consists of the germ cells that are set aside in the embryo at the blastula stage, which are incorporated into the gonads during organogenesis. The germ layers form during gastrulation of the blastula. Additionally, the term may refer to any ovum in which the blastoderm splits into three layers.
Simpler animals qualified as diploblastic, such as cnidaria (which includes jellyfish, corals and hydra), possess two germ layers. Even simpler animals, such as sponges, contain no true tissues. The body wall of sponges consists mainly of two layers, pinacoderm and choanoderm, and a non-cellular structure between these two layers called mesohyl.
Triploblasts emerged within the Diploblasts.
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