Antarctic icefish are the only vertebrates on Earth with no red blood cells and no haemoglobin, running clear plasma through oversized hearts in water so cold it would freeze the blood of every other fish that tried to swim there
Antarctic icefish are the only vertebrates known to live without haemoglobin or red blood cells, surviving in near-freezing Southern Ocean water by pumping clear plasma through enormous hearts and absorbing oxygen through scaleless skin.