These are Mesnilella, mouthless unicellular organisms that live inside the guts of certain aquatic worms. . Mesnilella has no cell mouth and gets its nutrients through diffusion; the worm eats and digests food in its stomach and guts, and Mesnilella hangs out there, almost basking in nutrients, letting simple molecules seep into its cell. . Mesnilella is part of a group called astomatid ciliates. A few hundred species are described in the literature, and they all live inside other organisms beca