Diatoms and cyanobacteria, both of which are moving around in a sample of pond water viewed under a microscope. You can see in the second picture that they have changed position (I wish I had filmed it!)
But how do they move around?
Diatoms are photosynthetic algae enclosed in a silica shell. In the pictures above, they are the diamond-shaped cells that appear brownish-gold or green. Some diatoms are capable of secreting mucus and sliding around on it like a slug (sort of). Not all diatoms are motile, however. Many of them just float around or sink down into the sediment. For a video of diatom movement, click here.
Cyanobacteria are photosynthetic bacteria found in moist or aquatic environments. They are the thin green strands in the pictures. Movement is achieved through gliding back and forth by unknown mechanisms, although it is believed that they also secrete mucilage in order to move (like diatoms). I’ll see if I can upload a video later!