Small pockets of seawater form in low spots on the seashore or rocky coastline when the tide goes out. These tidepools may look like just a puddle of ocean water, but there's much more for the explorer who looks deeper. What's lurking below the surface of the water? Is it the deadly blue-ringed octopus? A Christmas tree worm? Or something else? Amazing sea life that bites, stings, pinches, or simply swims make up these fascinating underwater worlds.