This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
This curious creature, captured here under the microscope, is not a protist. It's an animal. An animal, in fact, that can be smaller than some unicellular microbes.
It's a rotifer, and its stock in trade is sucking tiny prey to their doom. These multi-cellular micro-animals -- which, let me emphasize again, are smaller than some single-celled ciliates and amoebae -- come complete with tiny pharynxes, nerve cells, stomachs, intestines, a complete gut that ends in an anus, gonads, and a foot with grasping "toes" which some can use to move.
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I draw your attention to this film because it won an honorable mention in the 2012 Nikon Small World in Motion Competition. The results were announced last week and there were many other winners, but this video was by far my favorite.
The most striking aspect, in my opinion, is the clarity with which it shows the rotifer's beating crown of cilia, called a "corona". You can almost feel the tickle of the bristles, were you able to run your hand across them. This corona earned rotifers their name; the term means something like "wheel-bearer".
If you were keen-eyed, you might also have noticed this particular rotifer followed Standard Imperial Protocol by dumping its waste before it
made the jump to light speed continued ruthlessly crushing prey. This would be the microbial equivalent of the elephant lifting its tail in full view of the natural history filmmaker.
There is something oddly mechanical about this indisputably organic little creature. The rotifer's mastax -- a muscular pharynx that constitutes the food disposal unit -- seems relentlessly gruesome: gnashing jaws "chug like pistons" (my wording from a previous post) as they grind up incoming goodies. And if the jaws chug like pistons, perhaps the "wheels" turn like gears (they don't actually turn, of course. The beating cilia just make them look that way). In the same previous post, I described a herd of them (some of them can move, inching along like leeches)"a swirling vortex of rotiferan doom, with their mechanical jaws snapping like clockwork at the bottom of each whirling trap" and I think you can see that in this video too.
Speaking of those jaws, each jaw is composed of seven hard parts. The business end kan be pretty nasti:
Assorted jaws of bdelloid rotifers. Creative Commons Diego Fontaneto/PLoS One. Click image for link and license.
Though it's not obvious in this movie, one other aspect of rotifer anatomy is worth mentioning. Rotifers often live inside a hardened, ornamented cuticle. The following video does a good job of showing off the shell when the little animal is startled (watch for its jaws here too):
I had two other favorite videos from the Nikon contest. The first, another honorable mention, if of cytoplasmic streaming in an onion root cell(this video will not permit me to embed it in this post). In this video, you can see the tiny vacuoles flow through the cell in the cytoplasmic lazy river of the cell. Perhaps in high school or college biology you saw something similar in a leaf of the water plant Elodea, which is only a few cells thick. Under the microscope you can watch its chloroplasts (much larger than the tiny vacuoles in the onion) drift by:
I also loved the following honorable mention video of ciliates grazing on bacteria. The bacteria have been dyed red. The ciliates are not dyed red. You can see them because their many stomachs (actually, food vacuoles here) are stuffed with their glowing red prey. They poke and prod like busybodies at the apparently spongy bacterial meadows. Enjoy.
