Blastopore. A blastopore is an opening into the archenteron during the embryonic stages of an organism. The distinction between protostomes and deuterostomes is based on the direction in which the mouth (stoma) develops in relation to the blastopore.uring maturation of some animals it evolves into the anus or the mouth; in others it is covered over and contributes to the canal joining the primitive gut with the cavity of the neural tube, the primitive nervous system. blastopore synonyms. blastopore usage examples and blastopore quotes.