Siberian luminous earthworms

They contain a novel form of luciferin:

Intriguingly, the luminous system of Siberian taiga earthworms is different from that of similar types of species, which means that not only have scientists found one more luminous protein, but they have made a step towards
decrypting the whole new luminous system.

Crucially it is revealed that 'the protein is simple in chemical synthesis, exceptionally stable and not toxic, which means it can be widely used in applied bioluminescence'.

Earthworms don't have eyes.  Do they have photosensitive cells somewhere on their bodies?   That would seem to be a prerequisite for developing this luciferin, because otherwise the luminescence would only be of benefit to voles and other predators.  I remember reading somewhere recently about reptiles or amphibians with photoreceptors on their tails which allow them to detect whether they are fully hidden within their burrows.