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Horseshoe crabs have blue blood due to hemocyanin, which is rich in copper. Their blood is also vital for medical research because it clots in the presence of bacterial toxins.
Octopuses have blue blood due to the presence of hemocyanin, a copper-based molecule that helps them survive in cold and low-oxygen environments.
These marine animals have purple blood because they also use hemerythrin to transport oxygen.
The peanut worm has purple blood thanks to a protein called hemerythrin. This protein is visible through its translucent skin, making its blood appear purple.
Icefish are unique in that their blood is colorless. They live in the frigid waters of Antarctica and have no hemoglobin, relying on oxygen dissolved in the plasma.
Leeches have green blood, a result of the pigment chlorocruorin. This pigment functions similarly to hemoglobin but gives their blood a green tint.
Similar to octopuses, spiny lobsters also have blue blood. Hemocyanin enables them to efficiently carry oxygen in deep-sea environments.