de Chambrier & Vaucher (1999) compared the proteocephalidean cestode Spatulifer maringaensis Pavanelli & Rego, 1989 from Hemisorubim platyrhynchos (Valenciennes) with similar specimens, which they described as S. cf. maringaensis, parasitising Sorubim lima (Bloch & Schneider) collected in the Paraná and Paraguay Rivers. No remarkable differences between these worms were found by these authors, except for the scolex diameter and a different infection rate in each fish host. In order to elucidate the taxonomic status of the fish cestode Spatulifer cf. maringaensis from Sorubim lima, type and voucher material of S. maringaensis from H. platyrhynchos, and voucher and new material recently collected from Sorubim lima in Argentina are described in terms of their internal morphology and tegumental surface. During the study, mature and gravid worms with smaller metascoleces were found among voucher specimens from both hosts and in the new material from S. lima. The number of testes in the type-material was difficult to assess, but it could be determined in the voucher material from the type-host as being within the range of the specimens from S. lima. Both taxa are morphologically identical and can therefore be considered as conspecific. The data on their parasitological indices support the idea that S. lima is the principal final host and H. platyrhynchos is a secondary final host. Spatulifer maringaensis is widespread throughout the Paraná basin. A comparison of the microthrix pattern of S. maringaensis with that of S. rugosa (Woodland, 1935) revealed that they have the same type of microtriches, but with a different distribution, size and density. Tumuli were observed for the first time in a Neotropical taxon. Some studies have shown that the microthrix pattern is useful for characterising and discriminating species of the Proteocephalidea, and it was used herein as a tool for determining the conspecificity of S. cf. maringaensis with S. maringaensis.

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.

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