These graceful winged sea snails are so admired for their looks that they are known as sea butterflies. It turns out that they share more with insects than just a name - they flap their wings under water just like flies. The tiny snails, Limacina helicina, are one species of zooplankton in the cold waters of the Arctic and Antarctic. Their heavy shell makes them sink like a rock when stationary - unless they secrete a mucous web that keeps them afloat. They have also evolved wing-like appendages for swimming. But exactly how they beat their "wings" and how that propels them was unknown.
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