BLUE-BLOODED CREATURES

If you cut most animals, blood comes out red. By contrast, many underwater creatures, like crabs and lobsters, octopuses and squid, bleed blue. Our blood is red because of a chemical called haemoglobin in our blood cells. Haemoglobin includes an atom of iron, which clings on to oxygen molecules. Blood cells containing haemoglobin then carry oxygen around our bodies, working like a bright-red delivery van inside our blood vessels. Blue-blooded creatures have a chemical called hemocyanin instead of haemoglobin. It works in a very similar way, using copper instead of iron. The copper atoms turn their blood blue.

Sepioteuthis commonly lessoniana, reef known as the bigfin squid, has blue blood