Triploblasty

Triploblasty is a condition of the gastrula in which there are three primary germ layers: the ectoderm, mesoderm, and endoderm.

Germ cells are set aside in the embryo at the blastula stage, and are incorporated into the gonads during organogenesis.

The term triploblast may refer to any egg cell in which the blastoderm splits into three layers.

Other animal taxa, namely the ctenophores, placozoans, and cnidarians, are diploblastic, which means that their embryos contain only two germ layers.

[3] The earliest triploblasts are thought to have evolved from the diploblasts at some time during the Proterozoic era, establishing themselves as a group prior to their diversification during the Cambrian explosion.