archenteron A primitive digestive cavity of the embryo at the gastrula stage of development in animals. It is formed by invagination of mesoderm and endoderm cells, opens to the outside by a blastopore, and finally develops into the gut cavity.

archenteron (gastrocoel) A cavity within an animal embryo at the gastrula stage of development. All or part of the archenteron eventually forms the cavity of the gut. It is connected to the outside by an opening (the blastopore), which becomes either the mouth, the mouth and anus, or the anal opening of the animal.