What is "chlorocruorin"

Chlorocruorin \Chlo`ro*cru"o*rin\, n. [Gr. chlwro`s light green + E. cruorin.] (Physiol.) A green substance, supposed to be the cause of the green color of the blood in some species of worms.
--Ray Lankester.

n. (context biochemistry English) a green respiratory pigment found in many annelids

Chlorocruorin is an oxygen-binding hemeprotein present in the blood plasma of many annelids, particularly certain marine polychaetes. Its affinity for oxygen is weaker than that of most haemoglobins. A dichromatic compound, chlorocruorin is noted for appearing green in dilute solutions, though it appears light red when found in concentrated solutions.

Its structure is very similar to erythrocruorin (which is likewise very similar to multiple subunits of myoglobin) and it contains many 16-17 kDa myoglobin-like subunits arranged in a giant complex of over a hundred subunits with interlinking proteins as well with a total weight exceeding 3600 kDa. The only significant difference between chlorocruorin and erythrocruorin is that chlorocruorin carries an abnormal heme group structure. This enormous macromolecule is typically found free floating in the plasma, and not contained within red blood cells.