Hemocyanin is a protein found in many mollusks (some bivalves, many gastropods, and cephalopods) and arthropods (many crustaceans, some arachnids, and the horseshoe crab, Limulus).
This Protein carries oxygen in much the same way as haemoglobin carries oxygen in human blood.
Similar to haemoglobin, a central metal atom binds oxygen differentially, however, in hemocyanin, this central metal atom is copper.
The structure and function of the hemocyanin molecule revolve around the two copper atoms embedded at its core.
They are colourless when deoxygenated but turn blue on oxygenation.
Typically, hemocyanins have a high molecular weight.
The subunit of hemocyanin has a tendency to aggregate.