part of develops from capable of ommatidial precursor cluster retina ommatidium One of the facets of the compound eye. It is composed of eight light-sensing photoreceptor cells (photoreceptor cell R1-R8) and accessory cells. There are around 800 ommatidia in each compound eye. UBERON:0000971 FBbt:00004510 fly_anatomy.ontology VFB:FBbt_00004510 photoreceptor external sensillum adult head sensillum detection of light stimulus involved in visual perception