In which specific developmental stage is the archenteron cavity found?
Blastula
Gastrula
Morula
Planula
The archenteron cavity is found in the Gastrula stage of development. During this stage, the embryo undergoes significant changes including the formation of a primitive cavity called the archenteron. This cavity develops from the invagination of cells in the blastula and later gives rise to the digestive tract of the organism. Therefore, the archenteron cavity is specifically found in the Gastrula stage. Hence, the correct answer is option 2.