Finally, our study provides strong evidence for photosensitivity being an ancient feature of apical organs. Remarkably, the opsins identified in cells in and around
the apical organ in Platynereis (Figure 6K,L), and also in
Terebratalia transversa [117] and Nematostella vectensis
[86], all fall within the peropsin/ciliary opsin families.
These observations indicate that apical organs evolved
as multimodal sensory structures, of which photosensitivity formed a key component.