Red blood cells, or erythrocytes, ... The immunological functions of nucleated erythrocytes are well-established in non-mammal vertebrates. In birds, amphibians, and fish, ...

Animal blood comes in a rainbow of colors—here’s why. From milky blue to lime green, organisms have evolved different types of blood—and ways to move oxygen around the body.

This is a photomicrograph showing a blood smear with the large red blood cells of the African clawed frog and the small red blood cells of a rodent side-by-side (400x magnification).