Compound eyes absent.

Compound eyes are absent. However, simple eyes (ocelli) may be present. Many insect orders have members that have lost the use of compound eyes e.g. parasites and cave dwellers. Some primitive orders (e.g. silverfish [Thysanura]) do not possess compound eyes or only have single elements of a compound eye present. Some advanced orders (e.g. lice [Phthiraptera]) have no use for complex eyesight and have reduced or lost their compound eyes.