Cleavage in zygote forms a hollow ball of cells known as a blastula. The blastocoel refers to the fluid-filled cavity present in the blastula stage of early embryonic development.
Blastula undergoes gastrulation during which some of the cells exhibit inward movement and form a sac. The blastopore refers to the opening of this sac present in the gastrula stage of embryonic development.
Blastopore of gastrula develops into the mouth in protostomes and becomes anus in deuterostomes.
