What is purple blooded?

"Purple-blooded" is a term often used to describe certain species of animals, particularly some types of mollusks and arthropods, that have a unique respiratory pigment called hemocyanin, which contains copper instead of iron. This gives their blood a bluish or purplish color when oxygenated, contrasting with the red color of vertebrate blood, which contains hemoglobin. The term can also be used metaphorically to describe people who are considered to be of noble or elite lineage.