Flatworms are flattened, leaf-like forms living in damp places on land, in freshwater streams of ponds, or along the seacoast while a variety of other species are parasitic. The free forms are usually small, barely reaching a length greater than five or seven cetimeters (2 to 3 inches). Some of the parasitic species attain the great length of six to thirteen meters (20 to 40 feet). This is a marine flatworm.
Winchell, Alexander Sketches of Creation (New York, NY: Harper & Brothers, 1870)