Images not to be used by the tobacco industry. Cuttlefish bone, coloured scanning electron micrograph (SEM). Cuttlefish are marine cephalopods who have a unique internal shell, made of aragonite, a carbonate mineral. They use this shell (the cuttlebone), to control buoyancy. The cuttlebone is porous, which allows for buoyancy, and the cuttlefish is able to regulate the level of buoyancy by altering the gas-to-liquid ratio in the many chambers that make up the cuttlebone. Magnification: x110 when printed at 10cm wide.