Noun
The word is derived from ommatidium
of Ommatidium
Source: Webster's dictionaryAeshna interrupta has 22650 ommatidia of two varying sizes, 4500 being large. Source: Internet
The compound eyes of adults develop in a separate region of the head. citation New ommatidia are added in semicircular rows at the rear of the eye. Source: Internet
Petalura gigantea has 23890 ommatidia of just one size. Source: Internet