While many forms are fixed to the substratum, others are free, being in this condition either motile or immotile.
The cause of this luminosity is Micrococcus phosphorens, an immotile round, or almost round organism.
Nearly all cocci are immotile, while the bacilli may or may not be.
immotile im·mo·tile (ĭ-mōt'l, ĭ-mō'tīl')
Not moving or lacking the ability to move.