Found swimming in a large, somewhat constant rain puddle. Tadpoles are also usually always in the puddle. This bug has a clear hard shell. It propels forward by twitching its tail downward. It constantly moves the comb-like structure in a wave-like motion at its base. It looks like eggs on their backs. They are lying on their side in the picture because the water is shallow, but they swim right side up like a regular fish.