Final answer:
During animal embryonic development, the opening created by the invagination of the gastrula is known as the blastopore, which serves as a precursor to the mouth or anus and is integral to the formation of the germ layers and primitive gut.
Step-by-step explanation:
The opening or hole created by invagination of the gastrula during embryonic development is called the blastopore.
Gastrulation is a critical phase in animal development, leading to the formation of the primitive gut, which eventually develops into the gastrointestinal tract. Inside the gastrula, the blastopore forms as an initial opening on one side of the embryo, which deepens to become either the mouth or the anus, depending on whether the organism is a protostome or a deuterostome. The germ layers, including the ectoderm, mesoderm, and endoderm, are also formed during this process. These layers will later differentiate into various organ systems through organogenesis. Specifically, the endoderm forms the digestive tract's lining, whereas the other two layers contribute to other critical structures within the organism.
The opening or hole created by invagination of the gastrula during animal embryonic development is called the blastopore. The blastopore is formed during a process called gastrulation, where the cells from the blastula move inward on one side to form an inner cavity that becomes the primitive gut (archenteron) of the gastrula stage. The blastopore can develop into either the mouth or the anus, depending on the type of animal.