• P. gracilis is distributed in the eastern United States, south of the Delaware River and east of the Missouri River.
• The animal are 8-30mm long and 1.5-6mm wide.
• The head is truncated at the anterior end with a slightly bulging frontal margin.
• The auricles are rounded and protruding laterally at the anterior end of the head.
• The coloration on the dorsal side is dark brown to almost black.
• The ventral side is somewhat lighter than the dorsal side.

Reference: R Kenk, Oceanography and Limnology Program (Smithsonian Institution), United States Environmental Protection Agency. Freshwater planarians (Turbellaria) of North America. Washington, U.S. Environmental Protection Agency, 1972.