Caryophyllidean tapeworms (Cestoda), Nearctic parasites of fish in Mexico, including description of a new species of and the first report of , an invasive parasite of common carp ().

The first survey of caryophyllidean tapeworms parasitising catostomid and cyprinid fish in Mexico is provided, including new host and geographical records. n. sp. is described from the Nazas sucker, Garman (type host), in Durango, Girard in Sonora, and Bean (Cypriniformes: Catostomidae) in Jalisco. The new species differs from congeners mainly in the shape of the scolex, which is rounded, and by the absence of a defined neck (distinct, often long in other congeners). found in (also a member of the family Catostomidae) from Oaxaca and Veracruz represents the southern-most report of species of this Nearctic genus. Three morphotypes of the holarctic Leuckart, 1878 were found in two leuciscid fishes ( and ) and in silverside sp. (Atherinidae). It is the first record of any caryophyllidean in atheriniform fish. The first record of (Yamaguti, 1934) (syn. Calentine et Ulmer, 1961), a parasite of common carp ( L.), in Mexico represents another evidence of its invasive potential. The caryophyllidean fauna of Mexican freshwater fish is depauperate compared to that in the United States and Canada, which seems to be related to a much lower number of species of suckers (Catostomidae) occurring in Mexico, possibly also to the lower number of fish in the population.