Two new Gyrodactylus (Trematoda: Monogenea) from cyprinid fishes with synopsis of those found on North American fishes

Gyrodactylus atratuli from the blacknose dace (Rhinichthys atratulus) and the pearl dace (Semotilus margarita) is compared with known species of Gyrodactylus from North American fishes and described as a new species. Gyrodactylus margaritae from the pearl dace (Semotilus margarita) is compared with known species of Gyrodactylus from North American fishes and described as a new species. The average number of G. atratuli per blacknose dace in the natural habitat is 7.8 (1 to 32) and in the laboratory at the same water temperature after 55 days in captivity, 5.4 (0 to 11). G. atratuli and G. margaritae fail to live and reproduce on fish kept in nonrunning water at between 19 and 26 C in laboratory aquaria, but will live and reproduce in running spring water at 12 C in laboratory aquaria. An illustrated synopsis with a comparative table of measurements of known North American Gyrodactylus and a list of the species with brief reference to their differentiating characteristics are given.