Respiratory pigment refers to a molecule within the body that binds to and carries oxygen. While the term respiratory pigment is commonly used in the scientific community, there are several alternative synonyms that can be used. Hemoglobin is a widely known respiratory pigment found in red blood cells of vertebrates, while myoglobin is a similar molecule found in muscles. Hemocyanin is a respiratory pigment found in arthropods and mollusks, while hemerythrin is found in marine invertebrates. Additionally, some organisms have adapted to use a variety of different respiratory pigments, depending on their environment and physiological needs, including chlorocruorin, which contains both iron and copper.