Triploblasty is a condition of thegastrula in which there are three primarygerm layers: theectoderm,mesoderm, andendoderm.Germ cells are set aside in the embryo at theblastula stage, and are incorporated into the gonads duringorganogenesis. The germ layers form during thegastrulation of the blastula. The termtriploblast may refer to anyegg cell in which theblastoderm splits into three layers.[1]
Allbilaterians, which are the animals with bilaterally symmetrical embryos, are triploblastic. Other animal taxa, namely thectenophores,placozoans, andcnidarians, arediploblastic, which means that their embryos contain only two germ layers.Sponges are even less developmentally specialized, because they lack both truetissues[2] andorgans.[3]
The earliest triploblasts are thought to have evolved from thediploblasts at some time during theProterozoic era, establishing themselves as a group prior to their diversification during theCambrian explosion.[4][5][6]
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