Some invertebrates have blue blood, too - literally. Oxygen is carried in their blood by a chemical called hemocyanin, similar to the familiar hemoglobin that reddens the blood of vertebrates but containing copper instead of iron.

The best-known example of a blue-blooded animal is the lobster, which is often consumed by aristocratic "blue blooded" humans, giving a bit of credence to the adage "you are what you eat." Others include the horseshoe crab, crayfish, scorpion, octopus, squid, clam and mussel.