If memory serves, fish in very cold ocean water (around 0 C) don’t have hemoglobin because at that temperature oxygen just dissolves into water. I assume their blood is clear.
Hmm so it requires a medium to exist…what if Amanu lived in a very thick miasma? I know they have communities and perhaps the air is unfiltered and in presence of so many god-like hyperintelligent fungi nerve cluster things surrounding them maybe it makes the air thick enough for that to allow to happen? Aaahh not sure