What is the color of blood? Your answer will be red, it isn’t since we have red blood and so are familiar with it. Besides human beings, vertebrates and mammals to have red blood cells due to the heme group (iron) of hemoglobin. However, there are some animals out there that have different blood colors like blue, green, yellow, orange, violet or even colorless blood. These different colors of blood results from plasma proteins in their blood.
Animals with blue blood.
Animals like cephalopods mollusks (e.g., squids and octopus) and arthropods like horseshoe crabs and spiders possess blue blood. Unlike hemoglobin found in the vertebrates, these animals have copper-containing respiratory pigments that help in the transportation of blood. Hemocyanin (Hc) is blue when it binds to oxygen, while pale yellow when it is not combined with oxygen. Hemocyanin occurs freely, dissolved in the hemolymph.
Interestingly, hemocyanin in octopus helps it to survive at extreme temperatures ranging from -1.8 degrees celsius to super-heated temperatures of thermal vents. Hemocyanin thus allows it to get a steady supply of oxygen.
Animals with green blood color.
We find it in worm-like animals, like Tobacco Hornworm, leeches, and skinks of the lizard family. Biliverdin is the dark green bile pigment responsible for this green blood color. Like humans, reptiles to have red blood cells rich in hemoglobin. When red blood cells break down, biliverdin, green-pigmented waste is made. This pigment is densely concentrated in lizards, making their blood appear green. We humans also have some biliverdin in our blood, but these lizards have about 40 times higher biliverdin levels in their blood. Leeches, however, have oxygen-binding protein chlorocruorin, making their blood green.
Animals with yellow blood color.
Yellow color blood for example in sea cucumbers is caused because of a high concentration of metal vanadium found in vanabin pigment. Ten percent of the blood cell pigment of the sea cucumber is vanadium. The exact role of vanabin is not known as like hemoglobin and hemocyanin, it does not have any role in oxygen transport. Indeed, sea cucumbers have hemocyanin to meet their oxygen requirements.
Animals with purple blood.
Marine animals like peanut worms have dark purple blood color and hence appear almost black. Hemerythrin is responsible for purple blood and helps to transport oxygen in marine invertebrates, however, it is only 1/4 as efficient as hemoglobin in binding oxygen. Blood appears purple when it gets oxygenated when oxygen is not bound it is colorless.
Are there any animals with colorless blood?
Yes, there are animals out there whose blood is colorless, one such is Antarctic ice-fish, the only vertebrate that lacks RBC’s, thus their capacity to transport oxygen is about 90% less than organisms having red blood. Still, they can survive as Antarctic water is oxygen-rich and have a very huge heart that ensures a sufficient supply of oxygen. Its blood also has antifreeze proteins circulating in their body, preventing ice crystals to form in their blood.
Animals that lack blood.
There are certain animals that lack blood for example flatworms, nematodes, and cnidarians like jellyfish, sea anemones and corals. These all lack a circulatory system and hence the blood. They meet their oxygen requirements by diffusion of gases by their body surface.
Thus, variation in the blood color of the terrestrial animals is because of the differences in the metallic component of the blood.
