Required for photoreceptor cell morphogenesis. Mediates homophilic cellular adhesion. Extracellular surface of R-cell plasma membrane. Expressed in photoreceptor cells and their axons in the adult retina, the ocellus and larval photoreceptor organ. Expressed 24 hours after initiation of photoreceptor cell differentiation, persists through development to adulthood. Belongs to the chaoptin family.