Horseshoe crab blood contains an oxygen-carrying protein called hemocyanin. Hemocyanin contains copper, which makes horseshoe crab blood bright blue in color. (Similarly, human blood is red because of the iron present in our hemoglobin.)
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Horseshoe crab blood contains an oxygen-carrying protein called hemocyanin. Hemocyanin contains copper, which makes horseshoe crab blood bright blue in color. (Similarly, human blood is red because of the iron present in our hemoglobin.)