The largest red blood cell (RBC) in the animal kingdom belongs to an amphibian called Amphiuma. It is 65 um in diameter and has a volume of 14,000 fL. What selective advantage was/is there for an RBC with such a long intracellular diffusion path length? These gigantic cells traverse equally large capillaries. That means there is less contact between the RBC and endothelium, further reducing O2 diffusion.1 One thing is certain: these creatures are highly successful, having survived the rigors of natural selection. They did something right… and those Goliath-like RBCs work just fine for them!!
