Red blood cells are ________, meaning that they do not have a nucleus.

Red blood cells, also known as erythrocytes, are classified as anucleate. This term specifically denotes that they lack a nucleus, which is a distinctive feature of mature red blood cells in mammals. The absence of a nucleus allows more space within the cell for hemoglobin, the protein responsible for oxygen transport, thereby enhancing the oxygen-carrying capacity of the blood.

While erythrocytes is an appropriate label for red blood cells, it does not specify the absence of a nucleus. Granulocytes and monocytes refer to different types of white blood cells, which do possess nuclei and serve various functions in the immune system. Therefore, anucleate is the most precise description for red blood cells in terms of their structural characteristics.