Re: can you give me examples of animals having blue blood ?

Hello Yadu,

As you probably know, our blood is red because the oxygen-carrying pigment in our blood cells, hemoglobin, is iron-based. However, hemoglobin is not the only respiratory pigment found in the animal kingdom. In fact, two of the largest (in terms of species number) groups of animals, the Mollusca and the Arthropoda, have blood that contains the pigment hemocyanin.

Hemocyanin is a respiratory pigment that is copper-based, rather than iron-based. When deoxygenated, hemocyanin is colorless; when carrying oxygen, it is a pale blue color. Incidentally, it is this pale blue, or cyan, color that gives the pigment its name.

Compared to hemoglobin, hemocyanin is a rather poor respiratory pigment. In other words, hemocyanin is not as good as hemoglobin at binding oxygen molecules at low concentrations of oxygen. Many of the familiar mollusks (e.g., clams, snails, and slugs) and crustaceans (e.g., crabs, lobsters, etc.) are sluggish animals and the relative inefficiency of hemocyanin suffices for them. Even the more active mollusks (squids, octopuses) and arthropods (flying insects) have hemocyanin as a respiratory pigment, and thus all these animals can be considered blue-blooded.

•Comparison of hemoglobin and hemocyanin. This page concerns hemoglobin, but there's a succinct comparison between the two pigments at the bottom, as well as information on the structure of respiratory pigments.

•A page that compares general biology of vertebrates and invertebrates. Despite the fact that all of the invertebrates are unfairly lumped together, this page does do a good job describing various invertebrate circulatory systems and the associated respiratory pigments.

I hope this answers your question!

Allison J. Gong
Mad Scientist