Hemocyanins are copper-containing oxygen carriers occurring freely dissolved in the hemolymph of many mollusks and arthropods. Composed of 3 major subunits (IB, II and III) and 1 minor subunit (IA) which form homohexamers and heterohexamers. May also form larger structures. Hemolymph. Belongs to the tyrosinase family. Hemocyanin subfamily.