The creatures, also known as pteropods, were photographed by Karen Osborn, a research zoologist with the Smithsonian Institution. They're related to snails and use a muscular foot to swim through the ocean.
Osborn found all of the pteropods off the coasts of Mexico and California and photographed them in a shallow tank of clear water to "inspire interest in these weird, wild animals," she told Smithsonian Magazine.
Many pteropods have shells made of calcium carbonate and are vulnerable to changes in the ocean's acidity. A study released earlier this month said the average surface acidity in oceans worldwide is 30 percent higher than at the start of the industrial revolution and the Smithsonian wrote last year that many shelled creatures in the Arctic have already started dissolving.
But while they're still here, take a look at more incredible images of the sea butterflies below: