Red blood cells (Erythrocytes) have no nuclei, mitochondria, or other organelles when they are mature. These organelles are ejected when the erythrocyte enters the bloodstream or shortly after. 

Should erythrocytes still be considered eukaryotic cells?

What do you predict would be the effects of having no nucleus?

In erythrocytes, the lack of mitochondria is an advantage. Why do you think this is true?