http://www.ucmp.berkeley.edu/platyhelminthes/dugesiasm.jpg
these "Flatworms" are unsegmented and bilaterally symmetrical. they typically appear as small white "worms" seen crawling all over the glass and ornaments, especially at night.
Planaria commonly show up in tanks with an excess of food and most are introduced to an aquarium from other aquaria with live foods like black worms, live plants, or anything else moved from an active aquarium that has them. If a lot of residual food is left in a tank, including dead and dying fish, snails, other animals, and plants, then a few planaria may divide into hundreds very quickly. they usually reproduce by asexual fission.
If a tank is found to have planaria, they can be controlled by a good vacuuming of the gravel and better tank maintenance. to remove planaria from a more heavily infested tank:
1. Set out bait like meat in a mesh bag. remove the bait a few hours after the lights go out on the tank. it should be covered with planaria. throw away and repeat until the population goes down.
2. add planaria eating fish to the tank. such species include the paradise fish, betta, pelvicachromis pulcher and many species of gourami
3. vacuum the gravel very well and do a 50% water change. often, planaria proliferate when the tank is too dirty. this will remove not only some planaria but their food source as well.
4. reduce the foods added to the tank. planaria often proliferate if too much excess food is provided.
just kidding on the sticker thing... do large gravel vacs and big water changes
at work, early childhood care and education center, and the kids wanted to make the tank pretty. They named the fish nemo, dori and bruce...guess what movie they had seen lol.