This plant is called Utricularia, also known as Bladderwort. Like the Sundew and the Venus Flytrap, Bladderworts are carnivorous plants. They trap insects and other small creatures as a source of nutrients (NOT energy!) The tiny, round bladders are the traps. Each bladder has a flap that opens and closes. When the flap is closed, the plant produces a low pressure inside the bladder. When something brushes the flap, it opens. The higher pressure of the surrounding water pushes water and whatever touched the flap into the bladder. Then the flap closes and the creature is trapped. The whole process takes less than 1/100 of a second. The trapped insects are source of nitrogen for the plant.