Nematocytes, cnidarian stinging cells, discharge nematocysts into prey to capture them. As nematocysts are expensive, the discharge is tightly regulated and occurs after proper chemical and mechanical stimulation. Here, I present evidence for nematocytes photosensitivity. I found
that light decreases the propensity for nematocytes to discharge in the sea anemone Haliplanella luciae. Taken together with similar findings in cubozoan and hydrozoan, we believe that light modulates nematocysts discharge for all classes of Cnidaria. I also investigated the effect of light
conditions, when combined with N-acetylated sugar Mucin, previously shown to sensitize nematocytes to discharge. Light and sugar seem to have separate and opposing effects on the propensity for nematocytes to discharge. We have preliminary evidences for a prevalence of the chemoreception over the light perception but further investigations should be conducted. Finally, our findings may suggest the involvement of an inhibitory G-protein in the sea anemone phototransduction pathway. While nematocyte chemo- and mechano-sensitivity have been extensively studied, we believe this is the first evidence for nematocytes sensitivity to light intensity.