title: Geographical variation in some representatives of Haematoloechus Looss, 1899 (Trematoda:Haematoloechidae) from Canada and the United States.
mesh_terms: D000818:Animals; D002170:Canada; D014644:Genetic Variation; D011898:Ranidae / Q000469:parasitology; D014200:Trematoda / Q000033:anatomy & histology* / Q000145:classification; D014481:United States