The archenteron is an indentation that forms early on in a developing blastula. In deuterostomes, the archenteron's beginning (where it invaginates) becomes its anus, and where it eventually connects with the other end of the gastrula becomes the animal's mouth. In protostomes, the opposite occurs: the first invagination becomes the mouth and the final connection with the external membrane becomes the anus. This is a determining factor used for animal classification as either a protostome (if the mouth develops first), or a deuterostome (if the anus devolops first).

The archenteron is known as the primitive gut that forms during gastrulation in the developing embryo. The indentation that is actually formed is called in amphibians and fish, the blastopore lip, and in birds and mammals it is called the primitive streak. Each is controlled by the dorsal blastopore, and primitive node, respectively.

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• Diagram

Developmental biology

Arquêntero