Did you know that a horseshoe crab has blue blood?

A horseshoe crab is an arthropod (arthropods have their skeleton on the outside rather than internally like humans) and belongs to the group known as “swordtails.” The horseshoe crab is also called a Moluccan crab or arrow crab. Contrary to what these names might suggest, the horseshoe crab is not a true crustacean but is more closely related to spiders. The blood of a horseshoe crab contains hemocyanin rather than hemoglobin.

Hemoglobin is based on iron, and when it reacts with oxygen, it causes the blood to turn red. The hemocyanin in the blood of a horseshoe crab contains copper. When this reacts with oxygen, the blood turns blue rather than red.

Interestingly, the horseshoe crab is the longest-existing species. It has been around for more than 400 million years. It has survived all the calamities over millions of years by living in stable areas where the environment changed little despite the disasters.

There are also other animal species with blue blood. Think of snails, octopuses, crabs, lobsters, and spiders, for example.

The image with this article is made bij Kyle Hartshorn via Flickr.com