Redescription of Parspina argentinensis (Szidat, 1954) (Digenea: Cryptogonimidae) from freshwater fishes (Pimelodidae) in the basins of the Paraná and La Plata Rivers, Argentina, with comments on P. bagre Pearse, 1920.

The type-specimens of Parspina argentinensis (Szidat, 1954) from Pimelodus maculatus Lacépède, and new material from Iheringichthys labrosus (Lütken), Parapimelodus valenciennis (Lütken), Pimelodella gracilis (Valenciennes), Pimelodus albicans (Valenciennes), P. argenteus Perugia and P. maculatus caught in the basins of the La Plata and Paraná Rivers, Argentina, were studied to elucidate its taxonomic status. The type-specimens of Parspina bagre Pearse, 1920 from Pimelodella metae Eigenmann in Lake Valencia, Venezuela, were also studied and new observations on its morphology recorded. The amendation of the generic diagnosis of Parspina Pearse, 1920 is proposed based on the study of both species, which revealed, among other features, the absence of a thin walled-membrane enclosing the male terminal genitalia. Parspina argentinensis is characterised by the following features: absence of a gonotyl; presence of a bipartite seminal vesicle, pars prostatica and ejaculatory duct; caeca of nearly equal length; uterus extending from the level of the ventral sucker to end of body; testes symmetrical to slightly oblique; ovary transversely elongate, compact and variable in shape; and the utilisation of a wide range of freshwater fishes as hosts. The tegumental surface of this species is covered with pectinate spines arranged quincuncially. Spines decrease in size and density from forebody to hindbody. There are two types of sensory papillae, ciliated and dome-shaped. Ciliated papillae are distributed on the surface of the oral region and on the dorsal and ventral surfaces of the body, whereas dome-shaped papillae are found on the surface of the ventral rim of the oral sucker associated with a ciliated papilla. Gland-duct openings are interspersed with the spines of the oral crown. In addition, the infection indices of P. argentinensis vary widely, not only among different hosts but also between the Paraná and La Plata River basins. Higher prevalences of P. argentinensis are recorded in the La Plata River, and Pimelodus albicans, P. maculatus and Iheringichthys labrosus are the principal final hosts in this area.