Gastrotrichs

Gastrotrichs. Without a microscope you'll miss these flattened stocky wormlike critters, because most of them are 0.1 to 1 mm. (A very few marine gastrotrichs get to be 4 mm. long.)  Gastrotrichs are covered with scaly or spiky hairs: Gastrotrich means "hairy belly", the kind of scientific name that's handy for your dissing vocabulary. They move rapidly on cilia, stretching and bending with the aid of some simple muscle fibers, as you can see in a video clip. Search "gastrotrich" ay YouTube for more. At their rear end the most familiar freshwater species divide into two tapering tails that end in tubular cement glands that help them temporarily stick in one place. All the freshwater gastrotrichs are parthenogenetic females. No males have ever been seen.
 
I found my first gastrotrichs in the very first sample of Java Moss I put under the 'scope, but you'd also find them in the floc of fine sediments where they hunt bacteria and algal cells that they suck in by a rapidly pumping pharynx that you might mistake for a heart.
 
Gastrotrichs develop from eggs, or they can produce thick-walled drought-resistant eggs that can remain dormant for long periods of time. Gastrotrichs have a mysterious evolutionary history.