develops from develops into ommatidial precursor cluster five-cell ommatidial precursor cluster Ommatidial precursor cluster composed of five photoreceptor precursor cells; R8, R2, R5, R3 and R4. This precursor cluster is formed when the mystery cells leave the cluster to rejoin the surrounding, unpatterned epithelium. The nuclei of the remaining cells rise apically whereas the nuclei of the surrounding cells descend. five-cell ommatidial precursor FBbt:00001771 fly_anatomy.ontology immature eight-cell ommatidial precursor cluster early ommatidial precursor cluster