It's called a Pikaia and it's a little wormlike creature but it's thought that this is a chordate, and that is the branch of life that we're in, so it could that this is our earliest known ancestor.
So eggs are laid in and around sources of water, and then, when it rains, or tides come into the wetlands, these eggs hatch, and out of these eggs hatch these wormlike larvae that swim around in the water.