to become the archenteron, a process driven by convergent extension. The open end of the archenteron is called the blastopore.

The filopodia--thin fibers formed by the mesenchyme cells, found in late gastrulation--contract to drag the tip of the archenteron across the blastocoel. The endoderm of the archenteron will fuse with the ectoderm of the blastocoel wall. At this point gastrulation