Tubifex Worms

Tubifex tubifex, also called the sludge worm, is a species of tubificid segmented worm that inhabits the sediments of lakes and rivers on several continents. These worms ingest sediments and gain nutrition by selectively digesting bacteria and absorbing molecules through the body wall. The worms can survive without oxygen for months, and can survive in areas so heavily polluted with organic matter that almost no other species can endure. By forming a protective cyst and lowering its metabolic rate, T. tubifex can survive drought and food shortage. Encystment may also function in dispersal of the worm.
Ecologically, it is important as a source of food for leeches, crustaceans, insects, and fishes. In a freeze dried, pelletised form, they are sold to aquarists as a form of fish-food. It is most economically important to humans as a host of Myxobolus cerebralis, which causes disease in fish stocks. No other worms are known to harbor this parasite.

T. tubifex probably includes several species, but distinguishing between them is difficult because reproductive organs, commonly used in species identification, are resorbed after mating, and because external characteristics of the worm vary with changes in salinity.