The blood carries oxygen effectively through a protein called hemoglobin which is present in red blood cells.
All vertebrates also have a protein called myoglobin that does not occur in the blood stream, but rather in the muscles. It is this protein that gives flesh its red colour.
Diving mammals have very large quantities of a myoglobin so much so that their flesh appears almost black. These large concentrations of myoglobin and resulting stores of muscular oxygen is one of the factors that allow these mammals to hold their breath for extended periods.
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