Why are some pond snails red?
A Compared to other habitats, ponds are naturally very low-oxygen environments. As a result, pond-dwellers have developed various adaptations to ensure that each and every breath counts.
Ramshorn snails are particular pioneers. Unlike most of Britain’s 40 or so freshwater snail species, all of which surface regularly to gather oxygen, members of this incredible family have come across an entirely new way of breathing. In contrast to most molluscs, which use copper atoms (hemocyanin) to transport oxygen through their cells, ramshorns, like humans, use iron atoms (haemoglobin) – and it’s this that gives their blood and bodies a red tinge. In all but the coldest environments, haemoglobin performs more efficiently than hemocyanin as a method of carrying oxygen around the body.
How the ramshorns hit upon this adaptation is not fully known. The snails’ haemoglobin molecules resemble those commonly stored in muscles tissues, suggesting that these molecules broke free from muscles and were later co-opted to assist in respiration.