Three trematodes (Monogenea: Dactylogyridae), Anonchohaptor muelleri, Icelanonchohaptor microcotyle, and Pellucidhaptor micracanthus spp. n., are described from Carpiodes carpio (Raf.) from the Missouri River in North Dakota and South Dakota. The generic diagnoses of Anonchohaptor Mueller, 1938, and Pellucidhaptor Price and Mizelle, 1964, are emended. The finding of Gyrodactylus dakotensis Leiby et al., 1972, Neodiscocotyle carpioditis Dechtiar, 1967, P. eremitis Rogers, 1967 (monogenetic trematodes), and Camallanus ancylodirus Ward and Magath, 1916 (nematode), from C. carpio constitute new host records. Also, 7 new locality records are established, 6 of which are reported for the first time from the upper Missouri River. The purpose of this investigation was to determine the helminth parasites of the river carpsucker, Carpiodes carpio (Raf.), in the Missouri River, its impoundments, and tributaries, in North Dakota and northernmost South Dakota, where it is considered a minor commercial species. Presently, 15 species of helminths are known to parasitize this fish (see Hoffman, 1967; Mackiewicz, 1963, 1969; Chien and Rogers, 1970). In our study, 13 species of helminths are recorded. Three new species are figured and described. MATERIALS AND METHODS One hundred twelve adult C. carpio (2 to 5 lb) were collected from 5 stations along the Missouri River (Fig. 1) and examined for helminths. The sampling area was comprised of approximately 400 miles of river from Mobridge, South Dakota, to Williston, North Dakota. Hosts were collected with hoop or gill nets by commerical fishermen from all stations except station 3 where fish were taken by hook and line. For techniques and procedures of collecting and preparing specimens, see Leiby et al. (1972). Figures were drawn with the aid of a camera lucida. Measurements are in microns unless otherwise stated. RESULTS AND DISCUSSION Thirteen species of helminths were recovered. These include seven monogenetic trematodes (three new), two digenetic trematodes, two cestodes, one nematode, and one acanthoReceived for publication 4 January 1972. *This study was supported in part by Grant GY-9091 from the NSF. t NSF Undergraduate Research Participant, Iowa State University, Ames, Iowa. cephalan. Seven new locality records and four new host records are recorded.