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One class of the phylum Platyhelminthes or flatworms is free-living, that is, not parasitic. These are the Turbellaria. These soft, flat worms are widely distributed over land, sea and fresh waters. Among the orders of the class Turbellaria are the Neorhabdocoela, Allocoela, Catenulida, Macrostomida, and the subject of this website - Tricladida or Planarians.
Planarians are free-living, primarily carnivorous flatworms-with a three-branched digestive cavity. Planarians may eat other living, as well as dead, invertebrates, detritus or decaying organic matter, and some prefer diatoms. I feed my planarians egg yolk and bits of beef liver. It is fun to see their gastrovascular cavity filled with egg yolk after a big meal! Most are freshwater forms, but marine and terrestrial planarians exist. White, gray, brown, black, and green or sometimes transparent, planarians range in size from 1/8 to 1 in. (0.32 to 2.54 cm), although some tropical forms are as big as 2 ft (60 cm). Some species can regenerate severed parts of the body, in some cases even producing entire individuals from small pieces.
They are found beneath rocks, logs, or dead leaves in springs, spring brooks, ditches, wetlands, streams, and lakes. I caught many planarians with a bit of beef liver tied to a string and dipped in a brook in Hartford, Connecticut when I was growing up. My recent attempt to do the same in a Western Massachusetts stream produced no captives. They are sensitive to organic pollution but prefer moderate nutrient levels - do not use tap water or distilled water for these creatures - get some pond or stream water. Flatworms tend to be found in cold water environments although some species (nontriclads) will be found across all temperatures.
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