Malcolm Edwin McDonald 1981 <p>This key is the second in a series for identification of the helminths reported in waterfowl (Family Anatidae, Order Anseriformes). The first was a key to nematodes (McDonald 1974).</p> <p>The trematodes show the greatest variety of forms among the helminth parasites of waterfowl, including over half of all species reported; sometimes this group also includes the greatest part of the worms in a single bird. Over 500 species of trematodes have been reported in waterfowl. Almost all of these have been included in the present set of keys; it was not possible, however, to obtain the descriptions of a few forms (7 of 525).</p> application/pdf en U.S. Fish and Wildlife Service Key to trematodes reported in waterfowl reports