the.com/gills
the original breathing apparatus, extracting oxygen from water like it's nothing
human echoEmbryos briefly form gill-like arches before becoming jaws and ears
efficiencyFish gills extract up to 80% of water's oxygen
countercurrentBlood flows opposite to water for maximum oxygen grab
fungi tooMushroom gills make spores, not breath
crab trickSome crabs keep gills wet to breathe on land