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The world within a drop of water

Michael Shribak and Irina Arkhipova / Marine Biological Laboratory, Woods Hole

This colorful Nikon Small World photomicrograph shows a bdelloid rotifer, a creature commonly found in freshwater. Click through a slideshow of aquatic curiosities from the Nikon competition.

Shark Week may be winding down, but just when you thought it was safe to go back in the water, along comes a host of fearsome-looking creatures from the black lagoon ... or from your drinking water.

Our summer slideshow from the international Nikon Small World competition features aquatic organisms ranging from the bdelloid rotifer, which has gone without sex for more than 80 million years, to an embryonic bamboo shark.

Each year, the Nikon contest highlights pictures made with a microscope, and this year hundreds of entries were received from around the world. I was one of the judges who was given the job of whittling that field down to the top 20 and rating them in order. I'd love to tell you which image came out on top — but that will have to wait until the fall, when Nikon is due to announce the winners.

Between now and then, you and other Internet users will get a chance to choose your own favorite. The "People's Choice" part of the competition is due to begin at the Nikon Small World website next week.

The pictures may be pretty, but they also serve a scientific purpose: to explore the world within a drop of water. Take the bdelloid rotifer, for example: These critters are about a half a millimeter (0.02 inch) long, and yet they play a crucial role in keeping freshwater clean. They've even been employed to clean up municipal wastewater. If you drink unfiltered tap water, there's a good chance that you've been drinking in rotifers as well. Eeuuwww? Check out this report on AmateurMicroscopy.net and this article from the Hartford Courant for more about the rotifer and how it figures in the history of microscopy.

I'd take rotifers any day over some of the other critters seen through a microscope, such as water fleas and lice. Several pictures in our slideshow shine a spotlight on water fleas — such as Leptodora kindtii, which is widely found in lakes and can grow up to nearly an inch (21 millimeters) in length. The giant water fleas are mostly transparent, which comes in handy for avoiding the fish that prey upon them. We've included a picture that focuses on the flea's surprisingly complex compound eye. If you're heading to the lake this weekend, don't be surprised if you get the feeling that you're being watched.

Another type of aquatic bug, the Argulus fish louse, is a nasty fish parasite. Not the kind of thing you want in your aquarium — or in your drinking water.

Our slideshow is just the tip of the iceberg when it comes to the worlds within a drop of water. Check out the exhibits at the Micropolitan Museum, including the "Water Flea Circus," for an in-depth exploration. Wim van Egmond, the museum's curator, produced a couple of the images featured in our slideshow (including the Argulus' ugly mug). Don't miss the 3-D images featured on van Egmond's home page!

For still more glimpses of microscopic worlds, click through these galleries:

Connect with the Cosmic Log community by "liking" the log's Facebook page or following @b0yle on Twitter. You can also add me to your Google+ circle, and check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.