blastopores

Blastopore refers to the opening formed during gastrulation in animal embryos through which cells begin to involute and the archenteron, the primitive gut, is established. In the classic view, the blastopore originates at the site where the blastula indentation occurs and progresses to form the opening of the gut tube. The moving edge of the blastopore, the blastopore lip, plays a key role as cells migrate inward, generating the nascent gut and setting up the basic body plan.

Traditionally, the fate of the blastopore divides animals into two polarity groups. In protostomes, the blastopore typically becomes the mouth, and the anus forms later from a secondary opening. In deuterostomes, the blastopore usually becomes the anus, and the mouth forms from a second opening. There are exceptions and variations across lineages, and modern developmental biology emphasizes that segmentation and axial patterning depend on more than the initial opening alone. The concept remains useful for describing early gastrulation movements and axis establishment.

Blastopore is a central term in embryology and comparative anatomy, applicable to a wide range of phyla including chordates, echinoderms, mollusks, annelids, and arthropods. The word derives from Greek blastos ('bud') and pore ('opening'). Studying blastopore formation aids understanding of fundamental developmental processes such as invagination, involution, and the formation of the gut and body plan.