I would compare the kind of "eye" that these bacteria are more to the parietal eye: it detects light to allow movement toward that light (in the Cyanobacteria, to photosynthesize; in primitive animals, likely to find and eat the Cyanobacteria!)

I almost wonder if the genetic code for the parietal eye + pineal gland looks anything like the code for this bacteria's shell. There could be a continuous line of descendence, there.