What do horseshoe crabs and aristocrats have in common?
They both have blue blood!
In mammals the oxygen carrying molecules in the blood usually contain iron compounds called haemoglobins. The presence of iron produces the characteristic red colour of the blood. Horseshoe crabs are living fossils, virtually unchanged since the Devonian Period, 360 million years ago. Their blood uses a different molecule to carry oxygen. It contains haemocyanin, a copper-based molecule known as a respiratory pigment. Some haemocyanins have a very high affinity for oxygen, hence their function in the blood of the crabs.
Other creatures, such as sea cucumbers and sea squirts, have yellow-green blood, based on compounds of the metal vanadium. |
