Hemocyanins are copper-containing oxygen carriers occurring freely dissolved in the hemolymph of many mollusks and arthropods. Binds 2 copper ions per heterodimer. Heterodidecamer composed of A and B subunits, each containing 8 globular oxygen-binding functional units. Heterogenous decameric or multidecameric structures may also be formed. Hemolymph. Forms a thioether bond between 2 amino acids. Belongs to the tyrosinase family. Hemocyanin subfamily.