Here's an obscure phylum of microscopic freshwater
critters that can't swim, but stumble around
on leaves and detritus. Tardigrade means "slow step," and the Victorian
biologist Thomas Huxley dubbed them "water
bears," a name that has stuck. They're
all aquatic, though a water bear needs no
more than a film of water on a bit of moss.
Their powers of surviving drought and freezing
(down to the temperatures of interstellar
space if they're dry enough) are legendary;
waterbears have revived from some wetted
herbarium moss samples that were well over
a hundred years old.
I mention them though I've never seen them.
Typical water bears are 100 to 500 nanometers
long. But the chance of locating my tardigrades
was a fine excuse for getting a microscope.
Without a microscope you'll miss these flattened
stocky wormlike critters too, 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. 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.
