Tiny sea snails, often referred to as sea butterflies, have much more in common with flying insects than you might think, according to a new study. It appears the snails glide through Arctic waters by flapping their wings.
At first glance Limacina helicina looks like any other sea snail, equipped with a heavy shell that measures between one and four millimeters in diameter but they lack standard tiny legs. Instead, sea butterflies have wing-like appendages that propel through the water.
In the latest study led by David Murphy, a postdoctoral researcher at Johns Hopkins University, scientists used high-speed cameras to closely examine the unusual movements of these creatures for the first time.
"We looked at the wing kinematics – how it moves its wings in a figure eight pattern – and it's very similar to how a fruit fly beats its wings," Murphy told the Christian Science Monitor. "Then we measured the flow around the animal as it swims, and the sea butterfly uses one of the same tricks to generate extra lift that lots of tiny insects use. In this trick, called the 'clap and fling,' the animal claps its wings behind it and then flings them apart, sucking flow in between the wings. This creates tiny flow tornadoes, or vortices, at each wing tip, which helps to lift the animal."
This came as somewhat of a surprise to researchers who were used to the movements of zooplankton that have similar wing-like appendages but use them as paddles to push through the water.
Since sea butterfly morphology closely resembles that of flying insects, researchers suggest they are a "remarkable example of convergent evolution," a process where different, unrelated organisms exhibit similar features that function in nearly identical ways.
Nonetheless, "flying" gives L. helicina an advantage, as their wing-like appendages are more efficient than "rowing" appendages of other marine creatures.
The study was recently published in the Journal of Experimental Biology.
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