Components of the Blood | Boundless Biology
The iron reversibly associates with oxygen; in so doing, it is oxidized from Fe2+ to Fe3+. (b) In most mollusks and some arthropods, hemocyanin delivers oxygen. Unlike hemoglobin, hemolymph is not carried in blood cells, but floats free in the hemolymph. Copper, instead of iron, binds the oxygen, giving the hemolymph a blue-green color.