And not just "ehhh... it's kinda blue," this is full on That's Blue!
Horseshoe Crabs don't have hemoglobin, they have hemocyanin which is copper based, rather than iron. It's the copper compound that gives it the blue color.
This is an example how evolutionary mutations can give rise to vastly different characteristics. Good and useful mutations are passed on where thoes that aren't are "abandoned" by selective pressure.
As it turns out, copper blood is less efficient than iron blood, but it was "good enough" for the horseshoe crab. Other species that may have had it in the past, not so much.
Horseshoe Crabs don't have hemoglobin, they have hemocyanin which is copper based, rather than iron. It's the copper compound that gives it the blue color.
This is an example how evolutionary mutations can give rise to vastly different characteristics. Good and useful mutations are passed on where thoes that aren't are "abandoned" by selective pressure.
As it turns out, copper blood is less efficient than iron blood, but it was "good enough" for the horseshoe crab. Other species that may have had it in the past, not so much.
When the horseshoe crab's upside down,
You must flip it.
You must flip it.