Most of the tiny creatures in the sea, collectively called zooplankton, move themselves along by using their limbs to paddle. But the sea butterfly, a marine snail the size of a peppercorn, has long appeared to use winglike appendages to fly through the water.

After a detailed study of the snail, researchers at Georgia Tech reported Wednesday in The Journal of Experimental Biology that the sea butterfly flaps its wings the same way a fruit fly does, in a figure eight pattern that provides lift in the water in the way the wings of tiny insects do in air.

They saw for the first time vortexes around the tips of the wings that insect research had not been able to detect, according to David W. Murphy, the first author on the paper. Dr. Murphy, now a researcher at Johns Hopkins, said the sea butterfly’s motion was easier to see because insects flap their wings hundreds of times a second, while the sea butterfly has four to five wing beats a second.

Dr. Murphy built the apparatus used to study the sea butterfly for his doctoral thesis. The snail was one of many creatures used to test it, all “little one- to five-millimeter zooplankton,” he said.