The answer would be Haemoglobin.
The Haemoglobin is a red pigment found in RBCs of vertebrates that helps to transport oxygen to various tissues.
Vertebrate blood is bright red when it is oxygenated and dark red when it is deoxygenated. Some animals such as crustaceans or mollusks, use haemoglobin to carry oxygen instead of hemoglobin.
Hope This Helped!
