Transmission electron microscope of hemocyanin, a respiratory protein and pigment found in molluscs and arthropods. Like hemoglobin in mammals, hemocyanin is an oxygen carrying molecule. Each molecule is barrel-shaped appearing rounded end-on but oblong with transverse striations when seen from the side. Here, the hemocyanin molecules are from a marine whelk Burnupena cincta. They are a copper-containing protein (non-porphyrin) that occurs in solution in mollusc hemolymph "blood". Magnification Unknown.