Based on the light-reactive behavior of siliceous sponges, their intriguing quartz glass-based spicular system and the existence of a light-generating luciferase [Müller WEG et al. (2009) Cell Mol Life Sci 66, 537-552], a protein potentially involved in light reception has been identified, cloned and recombinantly expressed from the demosponge Suberites domuncula. Its sequence displays two domains characteristic of cryptochrome, the N-terminal photolyase-related region and the C-terminal FAD-binding domain. The expression level of S. domuncula cryptochrome depends on animal's exposure to light and is highest in tissue regions rich in siliceous spicules; in the dark, no cryptochrome transcripts/translational products are seen. From the experimental data, it is proposed that sponges might employ a luciferase-like protein, the spicular system and a cryptochrome as the light source, optical waveguide and photosensor, respectively.