1939 Haploporidae Nicoll, 1914 Microphalloidea Ward, 1901 Diplangidae Yamaguti, 1971 Exotidendriidae Mehra, 1935 Faustulidae Poche, 1926 Microphallidae Ward, 1901 Pachypsolidae Yamaguti, 1958 Phaneropsolidae Mehra, 1935 Pleurogenidae Looss, 1899 Prosthogonimidae Lühe, 1909 Renicolidae Dollfus, 1939 Zoogonidae Odhner, 1902 Plagiorchioidea Lühe, 1901 Auridistomidae Lühe, 1901 Brachycoeliidae Looss, 1899 Cephalogonimidae Looss, 1899 Choanocotylidae Jue Sue & Platt, 1998 Echinoporidae Krasnolobova & Timofeeva, 1965 Encyclometridae Mehra, 1931 Leptophallidae Dayal, 1938 Macroderoididae McMullen, 1937 Meristocotylidae Fischthal & Kuntz, 1981 Ocadiatrematidae Fischthal & Kuntz, 1981 Orientocreadiidae Yamaguti, 1958 Plagiorchiidae Lühe, 1901 Styphlotrematidae Baer, 1924 Telorchiidae Looss, 1899 Thrinascotrematidae Jue Sue & Platt, 1999 Urotrematidae Poche, 1926 Human digenean infections Only about 12 of the 6,000 known species are infectious to humans, but some of these species are important diseases afflicting over 200 million people. The species that infect humans can be divided into groups, the schistosomes and the non-schistosomes. Schistosomes The Schistosomes occur in the circulatory system of the definitive host. Humans become infected after free-swimming cercaria liberated from infected snails penetrate the skin. These dioecious worms are long and thin, ranging in size from 10 to 30 mm in length to 0.2 to 1.0 mm in diameter. Adult males are shorter and thicker than females, and have a long groove along one side of the body in which the female is clasped. Females reach sexual maturity after they have been united with a male. After mating the two remain locked together for the rest of their lives. They can live for several years and produce many thousands of eggs. The four species of schistosomes that infect humans are members of the genus Schistosoma. Non-schistosomes The seven major species of non-schistosomes that infect humans are listed below. People become infected after ingesting metacercarial cysts on plants or in undercooked animal flesh. Most species inhabit the human gastrointestinal tract, where they shed eggs along with host feces. Paragonimus westermani, which colonizes the lungs, can also pass its eggs in saliva. These flukes generally cause mild pathology in humans, but more serious effects may also occur. References Notes Gibson, D.I., Jones, A. & Bray, R.A. (2002). Key to the Trematoda, vol.1 Littlewood D.T.J. & Bray R.A. (2001) Interrelationships of the Platyhelminthes. Yamaguti, S. (1971). Synopsis of digenetic trematodes of vertebrates. Keigaku Publishing Co., Tokyo. External links Cambridge University Schistosome Research Group Parasitic Worms at the Natural History Museum, London Fishdisease.net Protostome subclasses