I thought this was an interesting article, so I'm copying and pasting it here. Link is below - the website is an eyesore, but worth muddling through.
http://www.fish-as-pets.com/2007/11/planaria-detritus-internet-answers.html
PLANARIA (often confused with Detritus Worms) and other Incorrect Internet Aquarium Answers
Updated 4/15/10
Detritus Worms (below)
Detritus Worms, white substrate worms, misidentified PlanariaThis post was/is inspired by the many questions I have read or been asked from readers of my articles or forum members (Everything Aquatic) as to Planaria, which most of the time have been misidentified (in sites such as Yahoo Answers, Aquarium Wiki, Aquarium Fish.Net, Fish Deals, or About.com) and are actually Detritus worms which are an "Annelid" not even closely relate to a Planaria. The other part of this confusion by these “cut and paste” sites/articles is even when correctly identified, Planaria are still attributed to the same water conditions that cause a Detritus Worm population “explosion” which is simply not true and can lead an aquarium keeper to address non existent problem if they believe this misinformation from sites such as Aquarium Wiki.
Sadly a Google search brings up these extremely inaccurate articles at the top, so these aquatic lies continue to be spread.
The problem with this confusion of these two very different worms is important since infestations of each of these different worms has very different implications for your aquarium, So Please Read On!
These Detritus Worms are normally not a problem and often go un-noticed living in the gravel aiding in breakdown of wastes. When the population explodes these worms often leave the gravel and cling to the sides, usually close to the surface as oxygen depletion due to the cumulative affects of increased organic mulm, cloudy water and simply too many Detritus worms drives them from the oxygen poor gravel. The population explodes generally due to high amounts of decomposing organic mulm (often resulting in cloudy water, pH drops, etc.), which is often an indicator of a tank with poor filtration, poor cleaning practices, too high of a bio load, poor Redox balance, poor feeding practices (not always over feeding, sometimes simply feeding foods that do not digest well) and other reasons as well.
For further information about the subject worms, please see my Aquarium Answers Blog post: * “Aquarium Answers; Trematodes and Nematodes in Aquariums” which includes information about these worms near the bottom of the article.
Planaria (below)
In the case of Detritus Worms, no one has bothered to check with any zoological, biology are similar research site. These article mills (and some department store type pet shops as well) just keep pumping out repeated misinformation built upon other misinformation. In the case of Detritus Worms (AKA Planaria, but incorrect) I checked several sources to confirm what was a baffling amount of poor information in aquatic sites, yet all the biology sites confirmed the rather obvious difference between Planaria and Oligochaetes Worms (the family of worms that compost in water that includes tubiflex, naidid, and similar worms.
Planaria are tiny flatworms that live in freshwater and marine environments, and on plants throughout the globe. Planaria live in fresh water ponds and is a carnivore. The pharynx (the passageway leading from the oral cavity in the head to the esophagus) can be protruded from the mouth which is in the middle of the ventral side of the animal. The diet consists of such foods as insect larvae, small crustaceans, and other small living and dead animals, Not decomposing matter as Detritus Worms do.
Planarians reproduce asexually and sexually; individuals have both testes and ovaries. A single one can be cut into hundreds of pieces and each will grow back into a whole planarian—a remarkable feat regenerative capacities.
The implication of a true Planaria infestation is VERY different from the much more common Detritus worm infestation, which is why this correct identification is so important. Planaria can harm some fry, fish eggs, or even occasionally resting or weak fish, and are generally not an indicator of a dirty aquarium as is the common myth.
Where as Detritus worms are primarily decomposters that cause little harm unless their population explodes which then they compete for oxygen with fish and are an indicator of poor tank conditions in general. When Detritus worms are out from the gravel crawling on the glass, etc, this is a sign of a “dirty aquarium” with implications of high amounts of mulm and lower dissolved oxygen as noted earlier.
Removal (Treatment) of Planaria:
There are several remedies that can rid a tank of Planaria, here are a few:
*Clout; this is probably the most effective treatment which contains 4-[p-(dimethylamino)-)O-Phenylbenzylidene]-2,5-cyclohexadien-1-xylidene dimethylammonium chloride; dimethyl (2,2,2-trichloro-1-hydroxy-ehtel) phosphonate; 1,2-dimmethyl-5 nitromidazole and inert ingredients as non toxic binders.
A negative of this treatment is it cannot be used with Piranhas, Metynnis species, scalelesss fish, bottom feeders, Marine Sharks, or Lion Fish
*General Cure; Not as strong, but still often effective and less harsh on delicate fish. General Cure contains Metronidazole & Praziquantel
*Jungle Parasite Clear; As with General Cure, not as strong as Clout, but still often effective and less harsh on delicate fish.
*Most Medications/Treatments that contain Trichlorfon (although this is very harsh on silver fish, arowana, and similar)
*Copper at .25 ppm can be effective for Planaria
Other references:
*
http://www.exploratorium.edu/
*
http://www.baruch.cuny.edu/