Hemoglobin
An iron-containing protein in the red blood cells of vertebrates that carries oxygen from the lungs to tissues throughout the body and gives blood its red color.
The Icefish is the only known vertebrate with no Hemoglobin or red blood cells at all, surviving on oxygen-rich frigid water and an enlarged heart and gills instead.
0
The Octopus's blood is blue, not red. Human blood is red because the iron-based protein Hemoglobin carries its oxygen; in octopuses that job falls to Hemocyanin, a Copper-based protein. Hemocyanin turns blue when it binds oxygen, and carries it better in the cold, low-oxygen sea.
0