Archenteron

The archenteron is an indentation that forms early on in a developing blastula. The archenteron will go on to develop into either the animal's anus or mouth. The fact that this develops in two different ways is used for animal classification as either a schizocoely or an enterocoely.

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 dorsal blastopore, and in birds and mammals it is called the primitive streak.