haemocyanin (hemocyanin) Any of a group of copper-containing respiratory proteins found in solution in the blood of certain arthropods (e.g. crabs and lobsters) and molluscs. Haemocyanins contain two copper atoms that reversibly bind oxygen, changing between the colourless deoxygenated form (CuI) and the blue oxygenated form (CuII). In some species, haemocyanin molecules form giant polymers with molecular weights of several million.

haemocyanin (hemocyanin) A blue, copper-containing, respiratory pigment that is found free in the blood plasma of molluscs and crustaceans. It is a non-haem compound that is a polymer of smaller monomeric units.