Sea Butterfly

Sea butterflies are tiny, free-swimming sea snails that spend their entire lives adrift in open ocean waters rather than crawling on the seafloor like most snails. Their foot has evolved into a pair of wing-like flaps that beat through the water in a fluttering motion, giving the group its common name and letting them swim continuously through the water column. Most species carry a thin, often nearly transparent shell of calcium carbonate, which makes them especially vulnerable to the more acidic ocean conditions caused by rising carbon dioxide levels.