Thousands of brown lines

William Hopkins Amos, Nature Program, Pond Life, National Audubon Society, New York, Nelson Doubleday, 1958, p. 15.

These small wormlike creatures usually inhabit bottom mud, or construct tubullar dwellings from bits of debris on submerged surfaces. Often a sunken log or rock will be covered with thousands of brown lines about a quarter of an inch long. Upon closer examination these are seean to be tiny mud tubes. If a tube is opened carefully, a larva will wriggle free.