This is a really nice video that was published in the Journal of Plankton Research this past February, as a part of this article about krill.
Even though krill make up a large fraction of the living mass of the ocean (and are also the food for large charismatic sea mammals), many aspects of their biology is unknown, including the way they reproduce. Recently Dr. Kawaguchi and his colleagues filmed the process happening near the sea floor, which was surprising because krill are notorious for living their lives swimming around up higher in the water, far from the floor.
The footage that the researchers collected was a bit chaotic (above, left), and so they gave it to Lisa Roberts, an animator (and CreatureCast contributor), to illustrate the process. She traced the motions of the crustaceans from the videos, and also practiced the moves with some shrimp from the market (above, right).
The original video footage from the deep sea is also really nice to watch, and can be found here, at the Journal of Plankton Research website.
The animation at the top of the post, and the drawing at the bottom, were made by Lisa Roberts and released under a Creative Commons Attribution Noncommercial Share-Alike 3.0 license. The soundtrack to the animation is by Graeme Ewing.