For the size of the skull, the teeth are rather small, and arranged in a primitive groove.

The song is "TV Eye," and they have gotten wickedly good at their primitive groove - as good as they will ever get.

This invagination expands posteriorly into the primitive groove as the cells layers continue to move into the space between the embryonic cells and the yolk.

A shallow groove, the primitive groove, appears on the surface of the streak, and the anterior end of this groove communicates by means of an aperture, the blastopore, with the yolk sac.