Chlorocruorin is an oxygen-binding hemeprotein present in the blood plasma of many annelid

Annelid

The annelids , formally called Annelida , are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches...

s, particularly certain marine polychaete

Polychaete

The Polychaeta or polychaetes are a class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. Indeed, polychaetes are sometimes referred to as bristle worms. More than 10,000...

s. Its affinity for oxygen is weaker than that of most hemoglobin

Hemoglobin

Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...

s. A dichromatic

Dichromatism

Dichromatism is a phenomenon where the hue of the colour in materials or solutions are dependent on both the concentration of the absorbing substance and the depth or thickness of the medium traversed...

 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

Erythrocruorin

Erythrocruorin is a large oxygen-carrying protein, whose molecular mass is greater than 3.5 million Daltons. It is related to the similar chlorocruorin. It is found in many annelids.- References :*, PNAS June 20, 2000. Accessed July 17, 2007....

 (which is likewise very similar to multiple subunits of myoglobin

Myoglobin

Myoglobin is an iron- and oxygen-binding protein found in the muscle tissue of vertebrates in general and in almost all mammals. It is related to hemoglobin, which is the iron- and oxygen-binding protein in blood, specifically in the red blood cells. The only time myoglobin is found in the...

) and it contains many 16-17kDa

KDA

KDA may refer to:* Karachi Development Authority* Kongsberg Defence & Aerospace* Kotelawala Defence Academy* Kramer Design Associates* Lithium diisopropylamide, KDA is the potassium analogue of lithium diisopropylamideOr kDa may refer to:...

 myoglobin-like subunits arranged in a giant complex of over a hundred subunits with interlinking proteins as well with a total weight exceeding 3600kDa

KDA

KDA may refer to:* Karachi Development Authority* Kongsberg Defence & Aerospace* Kotelawala Defence Academy* Kramer Design Associates* Lithium diisopropylamide, KDA is the potassium analogue of lithium diisopropylamideOr kDa may refer to:...

. Because of its giant macromolecule

Macromolecule

A macromolecule is a very large molecule commonly created by some form of polymerization. In biochemistry, the term is applied to the four conventional biopolymers , as well as non-polymeric molecules with large molecular mass such as macrocycles...

 structure, chlorocruorin is free floating in blood. The only significant difference between chlorocruorin and erythrocruorin is that chlorocruorin carries an abnormal heme group structure. This enormous macromolecule

Macromolecule

A macromolecule is a very large molecule commonly created by some form of polymerization. In biochemistry, the term is applied to the four conventional biopolymers , as well as non-polymeric molecules with large molecular mass such as macrocycles...

is typically found free floating in the plasma, and not contained within red blood cells.