Sea butterflies are a variety of snail that possess the unique ability to "fly" through the water, similar to the way insects travel through the air.
The creatures, also known as Limacina helicina, utilize wings that protrude through their shells in order to carry themselves through the marine environment. Until now, biologists were uncertain how the creatures moved themselves through the water.
The snails were carefully studied by a team of researchers as they carried out their daily activities underwater. Researchers constructed a system to precisely track how fluid moved around the minuscule creatures as they propelled themselves through the aquatic environment. Investigators found the animals moved their wings in a figure-eight pattern, in a manner reminiscent of airborne insects.
Sea butterflies are not common, and the tiny animals are fragile, making study of the creatures challenging. The mollusks needed to be shipped across the country to the research center in Atlanta, Ga. Once there, they were placed inside a tank of water, featuring a V-shaped tube at its base. Cameras placed at the center of the enclosure recorded movement of the animals as they rose out of the tunnel. Researchers only had a brief time to record the animals before water conditions declined. The snails made four good passes across the camera's field of view during the observation window.
"In this sort of free-swimming experiment it's normal to take 30 passes to get three usable ones, but we got really lucky! The animals even cooperated by swimming in different orientations, so we could see different perspectives," said David Murphy of the Georgia Institute of Technology.
Analysis of the data revealed the aquatic mollusks were moving their wings in a figure eight, much like the behavior of fruit flies. At the top of each stroke, the wings touch in order to increase the amount of lift produced by the wingtips during each stroke. In each case, the motion produces a low pressure system above the creatures, providing buoyancy.
Analysis of how sea butterflies utilize their wings to "fly" through the water like fruit flies through the air was published in the Journal of Experimental Biology.
