One very interesting organism found occasionally in aquariums is called a “slime mold” (Myxogastria). This is somewhat like a cross between an amoeba and a fungus. It can very slowly move overnight, forming new networks and structures with hyphae like a fungus. It can also separate into thousands of single cells which move away from each other, like amoeba, then regroup days or weeks later. It can form fruiting structures just like very small mushrooms. It is harmless.
When food is abundant, these slime molds exist as single-celled organisms. When food is in short supply, many of these single-celled organisms will congregate and start moving as a single body. In this state they are sensitive to airborne chemicals and can detect food sources. They can readily change the shape and function of parts, and may form stalks that produce fruiting bodies, releasing countless spores, which water currents will then disperse. The photo below shows the fruiting bodies:
They feed on microorganisms that live in any type of dead plant material. They contribute to the decomposition of dead vegetation and wood, and feed on bacteria, yeasts, and fungi. They do NOT indicate anything wrong in a tank and are not caused by over-feeding or bad water chemistry.
If a network of slime molds forming on a glass and is wiped or disturbed the remaining cells of the slime mold will form small worm like creatures on the glass. Some hobbyists will then come on social media with “what are these worms in my aquarium?” questions. If a “worm” has several irregular branches and doesn’t perceptibly move, it is a slime mold which has been disturbed.