The correct option is D Archenteron
The cavity of gastrula is the archenteron cavity which is formed by the invagination of cells. Gastrula is the stage where the morphogenetic movements and the formation of germ layers takes place. Coelom is the body cavity which is lined by mesoderm. Blastocoel is the cavity of blastula and chorion is an extra embryonic membrane which forms the placenta in mammals. So, the correct option is 'Archenteron'.