Is Erythrocruorin red? (aka earthworm blood color)

[Vree]

Some grade shool books claim that earthworm blood is red because it has hemoglobin, like ours.

Now right away you need to clarify what "hemoglobin" can mean. I'll start off by saying that IMO it is incorrect to use the word for every oxygen-transporting protein. Moreover it is false to assert that the oxygen-transporting molecule in earthworms is the same molecule that is found in our body. Therefore arguing the result with this method is false.

So what is the correct way to prove it?
Obviously, if you could say that the respiratory pigment in the worm (Erythrocruorin) is of a red color when oxygenated.

Funny thing is, I could never find any study that would confirm this, only the aforementioned "earthworms have red blood" ones.

Could somebody help to improve this popular misconception?

(& Also the Wikipedia article where this question already got asked by someone.)

 

[Tyrannosaurus_]

What is the oxygen carrying group? The colour of blood in humans is primarily the result of the oxidation state of the iron in haemoglobin. I'm not certain, but I think, that myoglobin - the oxygen transporting protein in mammalian muscles - is red in colour when oxygenated. Again, I believe this is due to the colour created by the oxidation state of iron at the core of the oxygen transporting proteins.

Likewise, in some organisms that use copper to transport oxygen, there blood is blue due to the oxidation state of copper. Copper oxide is blue/green.

I'm not certain. Here's a cool post from someone more knowledgeable than me: http://www.quora.com/Why-is-copper-oxide-green [Broken]