It is not just blue, it's not turquoise, it's not lapis, it's actually cerulean!

Happy Friday.

Here is something simple and straightforward.

Horseshoe crabs have blue blood. When it is circulating, it is a grey-white to pale yellow color, but once it is in open air, it turns bright blue.

Unlike human blood that contains hemoglobin (which in the presence of oxygen turns red), horseshoe crabs have hemocyanin. This copper-containing protein is how they carry oxygen throughout their bodies.