The correct option is
A Gastrula
- Blastopore is an opening through which the cavity of the gastrula i.e archenteron, connects with the exterior.
- This blastopore forms the mouth in the lower animals i.e the protostomes.
- In the higher animals, the deuterostomes, the blastopore forms the anus.
So, the correct answer is "Gastrula'.