In the sandy bottom of warm coastal waters lives Paracatenula—a small worm that has neither mouth, nor gut. Nevertheless, it lacks nothing thanks to Riegeria, the bacterium that fills most of the body of the tiny worm. Riegeria looks after its host—it is farmer, quartermaster and cook all in one. A research team researchers led by the Max Planck Institute for Marine Microbiology has now deciphered how the bacteria supply the worm with nutrition.