In embryos the tegmentum is the anterior half of the neural tube.

The small oral aperture is pear-shaped, and located in the anterior half of the cell.

The anterior half of the thorax upperside is separated from the remainder by a fine white line.

The anterior half of the body has 20-32 distinct large black spots or cross bars.

Hind wing: more uniform, slightly darker on its anterior half.

On the anterior half, the abdomen has red streaks laterally.

The anterior half of whorls is chestnut brown, the rest flesh colored.

The space between the sutures is brown in the anterior half.

It is caused by only the anterior half of the left bundle branch being defective.