drawing with diatoms..

...or maybe not. Popular wisdom has it that you can observe diatom motility with indian ink, which will slide off the mucilage the diatoms secrete and their movement will create disruptions in the brownian motion of the ink particles in the water.

Well, nice pictures, but I'm not convinced I've had a right lot of that going on.
It's hard to tell who is responsible for what here... watching them in real time was no more revealing...

And colonies of other people are putting on a better show in the mucilage department.

All-round winners of the 50µm mucilage sack-race today seem to be these filamentous guys

though like I say, it isn't all that clear.