Animals Whose Blood Isn’t Red

New Guinea's Green-blooded Skinks Herpetologists don't know why a group of small tropical reptiles need green blood, but the search for an answer just took an unexpected turn. New Guinea is home to multiple lizard species from the skink family with lime green blood. (Consequently, their tongues, muscles and bones are all various shades of green.)

Crocodile Icefish Crocodile icefish frequent brutally cold portions of the sea where the water temperature can plummet all the way down to 28.5 degrees Fahrenheit (1.9 degrees Celsius). That's below the point at which fresh water freezes. In extraordinarily cold water, red blood cells turn into a liability. Blood with a high percentage of these cells becomes dangerously thick and hard to circulate when the outside temperature gets too low.

Octopuses Hemoglobin is a key ingredient in the circulatory systems of nearly all vertebrate animals. Yet many spineless creatures use an alternative protein: Hemocyanin. Both are capable of binding to and transporting oxygen. But whereas hemoglobin contains iron atoms, hemocyanin incorporates copper. As a result, blood containing the latter protein looks markedly different from our human blood. When hemocyanin-rich blood becomes oxygenated, the copper turns it blue.

Horseshoe Crabs Mankind owes a great debt to the world's horseshoe crabs. Quite unwittingly, these marine invertebrates have become our allies in the endless fight against medical maladies. And it's all thanks to their wonderful blood. Despite the misleading common name, horseshoe crabs are not true crabs. They're more closely akin to spiders — and just like those arachnids, horseshoe crabs have blue blood filled with hemocyanin.

Blackfin icefish The blackfin icefish, an Antarctic species also known as the Scotia Sea icefish, has been discovered to have white blood.

What animal has purple blood? Peanut worms, which are a kind of marine worm, have purple blood. This is due to the presence of hemerythrin, an oxygen-binding protein.